Sign Up for Brew Email


Truckee & North Lake Tahoe's Independent Newspaper | Tahoe News | Tahoe Music | Tahoe Events

The Saga of the Quagga

Separating the invasive species science from the hyperbole


Below is a list of studies on the quagga and zebra mussels, and several links to studies referenced in the article. Click on the titles to view the full study or report.

Quagga Mussel Risk Assessment An experiment test of quagga mussel survival and reproductive status using Lake Tahoe water with a prediction of invasion into Western water bodies

Inventory of aquatic invasive species and water quality in lakes in the Lower Truckee River Region: 2012

The Ecological Society of America survey (pdf download) “A calcium-based invasion risk assessment for zebra and quagga mussels” commissioned by the U.S. Environmental Protection Agency: This study puts Lake Tahoe, Donner Lake, and surrounding lakes in the “very low risk” category for quagga and zebra mussel invasion. Less than 10 percent of the country is categorized as “very low risk.”

Potential Distribution of Zebra Mussels and Quagga Mussels Phase 1 Report A Report for the California Department of Fish and Game: “Researchers have generally used or recommended the use of 12-15 mg/L [ppm] of calcium or sometimes lower concentrations … However, the records at the lower calcium levels probably represent either misidentifications, limited or inaccurate calcium data, or non-reproducing sink populations recruited from upstream in higher calcium waters.”

Examination of Calcium and pH as Predictors of Dreissenid Mussel Survival in the California Water Project Prepared for the Department of Water Resources: “12 mg/L [ppm] is given as a threshold for possible long-term survival of adult dreissenid mussels, provided the pH is above 7.8. This conservative calcium value is based on experience from Lake Superior where the pH ranges from 7.9-8.2 but the average calcium level is 13 mg/L [ppm]. Lake Superior has only isolated pockets of dreissenid mussels along the shoreline, despite the fact that the first mussels were documented in Duluth Harbor more than 20 years ago”

Short-term survival and potential grazing effects of the New Zealand mudsnail in an uninvaded Western Great Basin watershed

Truckee Regional Aquatic Invasive Species Prevention Program 2011 Annual Report


Lake Tahoe (springtime nearshore average) - 9.16 ppm
(Note: Nearshore calcium levels are typically higher than the rest of the lake, and springtime calcium levels can also be elevated, since this is the period where runoff loads the nearshore with minerals and nutrients.)
Donner Lake- 5.16 ppm
Boca Reservoir – 3.09 ppm; 6.6 ppm
Stampede Reservoir- 2.75 ppm; 6.1 ppm
Prosser Reservoir- 4 ppm; 6.7 ppm
Martis Creek Reservoir- 5.5 ppm; 8.7 ppm
Independence Lake- 4 ppm
Marlette Lake- 3 ppm; 3.9 ppm
Spooner Lake- 25.9 ppm; 28.6 ppm

(Note: Where two readings are shown, they represent an early summer average reading and a late summer/early fall average reading in 2012.)
Inventory of aquatic invasive species and water quality in lakes in the Lower Truckee River Region: 2012, UNR

For nearly five years, the campaign against invasive species in the Lake Tahoe area has been spurred by the specter of the environmental devastation created by two mollusks — small, aggressively invasive bivalves called quagga and zebra mussels.

But an in-depth review of national scientific studies reveals that the poster child for local invasive species programs has almost no chance of surviving long-term in local waters. Millions of dollars have been spent trying to keep mussels out of Lake Tahoe, Donner Lake, and surrounding reservoirs, despite the fact that scientific studies suggest the prolific little bivalve can’t colonize these calcium-poor bodies of water.

A new examination of this science has derailed a mandatory boat inspection program that was scheduled to take effect this summer at Donner Lake. After passing an ordinance mandating fee-based inspections last August, Town of Truckee officials have backtracked and are now recommending that the mandatory inspections be put on hold as they investigate the scientific underpinnings of the program. Voluntary boat inspections are still scheduled to take place this summer at Donner Lake and Boca, Prosser, and Stampede reservoirs as they have in years past.

But the science also raises larger questions — questions about how limited and poorly funded local scientific research was able to trump national scientific studies on mussel invasion risks; and questions about how invasive species program advocates have taken limited and conflicting scientific information and, according to one critic, generated a distorted picture of a lake under imminent threat of mussel invasion.

The most critical factor for zebra and quagga mussel survival — and the reason Lake Tahoe and Donner Lake are among the nation’s most inhospitable lakes for mussel invasion — is the calcium content of the water.

Mussels thrive in calcium-rich waters, filtering out the element and using it to build their shells and support their basic metabolic function. Lake Mead, the southern Nevada water body where some of the dire, worst-case-scenario examples of mussel infestations have occurred, has calcium levels of 80 parts per million (ppm) and water hardness levels of 288 ppm. In these conditions, quagga mussels grow large, reproduce rapidly, and colonize aggressively.

But Lake Tahoe has calcium levels that are merely one eighth those of Lake Mead, and Donner Lake’s calcium levels are even lower —  less than half of the nationally recognized minimum calcium threshold for mussel survival. An average of three calcium readings last fall put Donner Lake’s calcium levels at 5.2 ppm, or about 15 times lower than Lake Mead’s concentrations. Despite those average calcium readings, the concentrations do fluctuate throughout the season and vary in different parts of the lakes. Some small areas of Tahoe’s shoreline have registered higher concentrations, including readings of 12.4 ppm at the Tahoe Keys Marina and localized elevated calcium readings of 24.1 ppm taken from the sediment of Asian clam beds in the Ski Run Marina. Spooner Lake is the lone local lake with lake-wide calcium levels high enough to support mussel invasion.

Numerous scientific studies say that zebra and quagga mussels cannot survive at calcium levels below 12 ppm. And even at 12 ppm calcium levels, test cases across the nation show that mussels do not flourish. In places like Lake George and Lake Superior, where borderline calcium levels of 12 and 13 ppm exist, mussels have been introduced, but have not colonized either lake.

But for years, Tahoe residents heard little about the science that showed Lake Tahoe and Donner Lake were at very low risk of mussel invasion. Instead, they heard stories about Lake Mead, with photos of quagga-encrusted boat propellers from the southern Nevada reservoir that is a starkly different habitat than the Sierra Nevada, and stories about the tens of millions of dollars of damage the creatures create. And when the public did hear about scientific studies, they heard mostly about one 51-day, low-budget study that for the last four years has heavily influenced invasive species policy in the Lake Tahoe region.

In 2008, with the science pointing to Lake Tahoe as being at “very low risk” of mussel invasion, according to the Environmental Protection Agency-commissioned “A Calcium-Based Invasion Risk Assessment for Zebra and Quagga Mussels” (see sidebar), a team of scientists received $20,000 to do a local experiment on the mussel’s ability to survive in Lake Tahoe water. Led by Dr. Sudeep Chandra, an associate professor of limnology and conservation ecology at the University of Nevada, Reno, the team transported eight mussels from the waters of Lake Mead to the UNR lab, and placed them in water taken from the Tahoe Keys in South Lake Tahoe. Tahoe Keys water is among the warmest, most calcium-rich and nutrient-laden water you can find anywhere in Lake Tahoe. Despite the fact that one mussel died and the rest were losing body weight by the end of the experiment, the study reported that, “The possibility exists for at least adult quagga to survive, grow, and reproduce in the Lake Tahoe environment …  the diligent monitoring of recreation vehicles (the major pathway for transfer of invasive mussels to inland lakes) putting into western lakes-of-interest is prudent. The assumption that western oligotrophic waterbodies low in calcium are at very low to low risk of quagga mussel invasion is not necessarily supported.”

The report did not research the full life cycle of quagga mussels, including the ability of vulnerable mussel offspring (called veligers) to survive in Tahoe. Studying the ability of mussels to reproduce in an environment is the true measure of risk, since the threat of mollusks is directly tied to their rapid colonization of an environment. A non-reproducing “sink population” of mussels would only survive for the animal’s three- to five-year lifespan.

Steve Urie, a long-time Donner Lake homeowner who has extensively researched the quagga mussel issue, studied the scientific process of Chandra’s laboratory experiment and found flaws in the process.

“The ‘study’ and its conclusion is equivalent to raising tomatoes in a Sacramento greenhouse, transplanting them in a Meyers’ garden in July, and noting that because the tomatoes were still alive on Labor Day that the Tahoe Basin would be a fine area for tomato farming,” wrote Urie in an article submitted to Moonshine Ink.

The report did recognize some of its own shortcomings. The risk assessment said: “It is possible that the individuals collected from Lake Mead had sufficient reserves for survival, and even moderate growth, in any (non-toxic) environment for the 51-day duration of the experiment.”

The fact that adult quagga mussels could survive in Lake Tahoe water for 51 days should not have been surprising. Tahoe’s own invasive species education material says that the mussels can survive for up to a month completely out of water.

“In Tahoe, adult quagga mussel can survive out of water for as long as 30 days!” says the website of Tahoe Keepers, a kayak and non-motorized watercraft inspection group affiliated with the Tahoe Regional Planning Agency.

The study even theorized that the mussels were possibly cannibalizing their own shells to generate enough calcium for survival.


Reader comments so far...

Rosamond's picture

Nevada Division of Wildlife has confirmed that they have found the invasive New Zealand Mudsnail in the Truckee River. New Zealand Mudsnails have made a mess of aquatic ecosystems all over the West since their invasion into Idaho in the 80s. As Dr. Sudeep Chandra has repeatedly stated, the need for inspections of boats coming into our region is not simply an issue of a single invasive species, but rather, it is a necessary program that should reduce the probability of any number of invasives making it into the lake and its surrounding water bodies. Unfortunately, your paper has chosen to use its pages to promote doing away with the inspection process in our area. I can only hope that your vociferous but myopic position on these matters is disregarded by the state agencies responsible for protecting our waterways. Ultimately, these ecosystems do not belong to us; they belong to our grandchildren. And I believe we as a society should do what we can to avoid squandering our grandchildren's inheritance. Apparently, you disagree.

Chris, Thank you for commenting on this article, and for the recent column you contributed to Moonshine Ink. I am glad that you, as a biologist and researcher, have lent your perspective to this issue. Unfortunately, I think you misunderstand and misinterpret the role of Moonshine Ink, and myself as the author of this article, in the discussion over invasive species. As a journalist, I am relaying the scientific background on invasive species, telling the story of the mandatory boat inspection program at Donner Lake, and relating the history of the local science that has been conducted on the issue. I do not "promote doing away with the inspection process in our area" or hold a "vociferous but myopic position" on the issue. I do, however, believe that public agencies and non-profits funded by taxpayer money should be responsible for answering questions about the scientific backing for enacting regulatory, fee-based programs. There are certainly very legitimate issues about how the invasive species program has been marketed to the public that deserve some questioning. The Town of Truckee passed an ordinance that said quagga and zebra mussels were an "imminent" threat to Donner Lake and surrounding waters. As a biologist with a technical understanding of water chemistry, you know this is incorrect. Perhaps more, not fewer, questions about the scientific justification of the program should have been asked at the outset of this process. Equally, the mandatory inspection program itself deserves some scrutiny. If invasive species truly are a grave threat to the ecosystem of Donner Lake, perhaps we should inspect more than one of the three boat launches at Donner Lake. Finally, I think a discussion of the thoroughness of the local science that has been conducted on the issue is in the interest of the public. Should we base a $1.5 million-dollar-a-year mandatory boat inspection program at Lake Tahoe on a $20,000 study that was conducted for 51 days on mature mussels that have proven they can live for nearly 30 days entirely out of water? Should we base a New Zealand Mudsnail risk level on a two-week study of a mud snail that has proven it can live out of water for three weeks? In my opinion, these are legitimate questions. If your opinion on the matter is that there are a lot of invasive species that may or may not be able to live at Donner Lake, our local reservoirs and in the Truckee River, and we should instate mandatory boat inspections to be safe rather than sorry, I respect that opinion. But even with that position there are many questions that remain. If Donner Lake is under imminent threat of invasive species invasion, should each paddle boarder and kayaker be inspected? What about wintertime boat inspections? As opposed to the unfounded allegations in your comment that I am somehow advocating the "squandering of our grandchildren's inheritance," I do care deeply about our ecosystem. Hyperbolized attacks and inaccurate statements like that comment about me are, in my opinion, one of the problems with the invasive species campaign to date. If we could stick to a constructive discussion about the actual threats to our local ecosystem, the science about invasive species, and the best methods to guard our local waterways from degradation, I believe the community would be much better served. Thanks for commenting on the article. I appreciate the dialogue. David Bunker
Rosamond's picture

The native mussels, Anodonta californiana, and Margaritifera falcata, have survived and evolved in our Northern Sierra waters for millennia. Of these, Anodonta was found in both Tahoe and Donner Lakes. I ate a few of these rubbery creatures as a kid, when we lived on the east end of Donner. They’ve become quite rare in Donner, (hopefully not due to my adolescent appetite in the 60s), and CDFG has not found any native mussels at all in their mussel surveys of Tahoe to my knowledge. Margaritifera still occurs in the Truckee and Walker rivers, in very low numbers. The genetic variability between the remaining small, highly localized populations of Margaritifera falcata is sufficient that, if they were mammalian species, we might be considering whether to call them separate subspecies or even species. Of course, in the event of a successful introduction of non-native mussel species, the aforementioned 2 genera would be competing with the non- natives. Extirpation (localized extinction) is an all too common result when specialized, non-compeitive western aquatic taxa have attempted to compete with aggressive generalist non-natives. Frankly, though, I suspect that these taxa may well be wiped out of Donner within my lifetime due to human disturbance of their habitat anyway. I mostly bring these genera up as an introduction to the concept of DEMES; localized populations with little genetic flow among populations or sub-populations, resulting in localized adaptations and, sometimes, speciation. The Quagga mussel shows a definite tendency toward genetic/physiological variability among regional invasive populations, which is stated in the study of Chandra et. al, but not reported in your articles in Moonshine Ink. Stepien et al (2002) showed that genetic variability is high in Quaggas, with marked genetic divergence between native European populations and invasive North American populations, as well as high variability among North American populations. As it turns out, the variation between North American and European populations is putatively expressed in variability between these populations’ Calcium requirements, with the Eastern North American populations exhibiting substantially lower Calcium requirements (20mg/L) than those of European populations (28mg/L) . The Chandra report explained this issue very clearly, but was ignored in your and Steve Urie's quagga articles for Moonshine ink. I'll be charitable and presume you simply forgot to point this out. This well documented variability is one very weighty reason that we should be cautious, and not presume that physiological requirements of populations in the most recently invaded Western North American habitats are identical to those of eastern North American Populations. As for your protestations regarding the cost of the Invasives program in Tahoe, David, approximately 1.5 billion Tourism dollars are spent within the Tahoe basin annually, which generates something to the tune of 150 million state and local tax dollars annually. Do I think that we should spend 1% of that money to reduce the probability of aquatic invasive species being brought into the most unique lake in North America via recreational boats? You betcha. I’ll continue to deconstruct your and Steve Urie’s assumptions, assertions, and misunderstandings in a series of posts as soon I have the time. Expect my presence in this forum for quite some time. Just the facts.

I am not quite sure what your argument is here, Chris. Are you saying that we should have boat inspections because quagga mussels might evolve into a species that can live in Donner Lake in the future? I am aware that the Eurasian quagga and the North American quagga have differing habitat requirements, but it should be noted that quagga mussels have been shown to have a higher calcium threshhold than zebra mussels (Jones, Ricciardi, 2005). Donner Lake's latest calcium readings were at 5 ppm. All reputable national science on the species says that quagga mussels cannot live in an environment with that little calcium. It is a question of public policy whether the Town of Truckee or other municipalities would want to enact regulations and enforcements based on the possibilities of future genetic mutations of an invasive species. I do think the issue of the genetic variability of the species would be a rich subject for future research.
Rosamond's picture

David, the thesis of your article is that there is "virtually no possibility of Quagga invasion" in Tahoe. I am merely laying the groundwork as to why the reading public and management agencies should not simply take your opinion article as an unequivocal account of the factual information. I'm not sure how you interpreted what I wrote as an advocacy of management decisions based on potential "future genetic changes" of Quaggas. The high degree of EXISTING genetic variability in Quaggas is in fact an important and to some extent unknown variable in the equation. As Chandra's paper explicitly stated, we do not know enough about the genetics and physiologic tolerances of the most recent Western North American invasion of Quaggas to be able to say with much certainty what the risk is of an invasion without experimental data from those actual organisms. This is, of course, why his group is being funded for the current round of studies on the matter. Lastly, I would like to ask you directly, as you've gone to some effort to repeatedly remind the reading public that you object to 1.5 million dollars being spent annually on boat inspections/aquatic invasive intervention in the Tahoe basin; Given the fact that tourism dollars alone in the Tahoe basin produce ~150 million dollars of state and local tax revenue annually, why would you object to spending what amounts to only 1% of that tax revenue to protect the lake from invasives? If you object to that level of funding for boat inspections, what, if any, level of funding would you deem "reasonable"? I have a number of other points to make regarding your opinions and interpretation of the conclusions of the Chandra study, which I'll get to later, but today is a rock climbing day.

Chris, If you are making the case that existing genetic variability in quagga mussels is creating a breed of quagga mussel that can live in low calcium water, you should probably back that up with some science. While you denigrate my article as an "opinion article," I have thoroughly researched and cited numerous nationally published scientific studies to back up the statements I made in my article. While you cited one study on the genetic variability, you have shown no evidence that this relates in any way to the quagga's ability to live in low-calcium waters. On the public funding issue, perhaps this will make sense to you. Being a journalist is similar in some ways to being a scientist. We research and present fact independent of our own personal opinions on topics. You completely misread me, when you say I "object to 1.5 million dollars being spent annually on boat inspections/aquatic invasive intervention in the Tahoe basin." My personal opinions on the topic are not injected into my article. I would hope the same of scientists. As a professional journalist, however, it is my job to ask questions about public policy when there is legitimate cause for question. Contrary to what you say, I believe that if $1.5 million is truly protecting Lake Tahoe from environmental destruction, that is clearly a very small price to pay. If, however, scientific evidence shows that the species we have been protecting ourselves from to the tune of $1.5 million a year is unable to live in Lake Tahoe or surrounding lakes and reservoirs, then I do think there are some legitimate questions about the program. Happy rock climbing Chris. I enjoy the discussion. David Bunker

Regardless of if the Quagga and zebra mussel can survive and reproduce in the waters of Donner and Lake Tahoe doesn't mean that we should halt the inspections since there are plenty of other aquatic invasive species (AIS) that can be introduced into our lakes. It seems to me that David is just trying to point out that the public has possibly been mislead by what the actual threat of an invasive mussel infestation could be, since these mussel have become the "poster child" for the AIS program in our region. I don't know specifically what AIS Donner Lake already has in it besides for the Asian clam, but Tahoe has invasive weeds that can be spread between the two lakes very easily. Then there's Fallen Leaf Lake, which has a mandatory washing stations for all boats including non-motorized to keep Tahoe's invasive species out of Fallen Leaf Lake. Of course, there's the New Zealand Mud Snail being found in the Lower Truckee River, where does the water in the Truckee come from??? Maybe the snail should be the new "poster child". I'd like to know what the calcium levels of the Boca/Stampede/Prosser reservoirs are. Reservoir systems are very different from natural lakes, and Lake Mead is a reservoir.

I just saw the calcium levels listed above. No need to answer that question.

What was the Truckee Council's logic when they imposed inspections on Truckee's public town ramp, but neglected to require inspections on privately owned boat ramps? Groupthink? Do invasive species somehow not attach to boats owned by members of private homeowner associations (HOA's)? Are there any financial or other connections (or conflicts of interest) between the Town Council members and the private HOA's in town? "At Donner Lake, boat inspections have only occurred at Donner Lake’s public boat ramp. The other two heavily used ramp facilities — Tahoe Donner’s marina and a homeowners’ launch on the west end — have had no boat inspections."

Thank you, Mr. Rosamond, for understanding the scientific process, and attempting to painstakingly point out to this "journalist" that one cannot simply find a few articles that are convenient to ones point and call it research. I especially like when the "journalist" attempts to put you down for only citing one article, while he has found a few. Does he want an "attaboy"? Sure, journalism and science could potentially be comparable, but not in this case. Science requires accountability and the compilation of all available data, not just one set of numbers taken out of context. It is your job as a journalist to provide all of the facts. Perhaps you are finding yourself a little out of your league here? As for Steve Urie, the only thing he, and the writer of this article, have managed to articulate is that the need for science education in this country is astounding. These "articles" was deeply upsetting to me as a scientist, intelligent woman, and Tahoe area resident. They should be discounted by all who read them. If you are reading this, and would like to find out more information about invasive species, please turn away from these articles and check out or any of the amazing local agencies around the Tahoe area! Thank you, again, Mr. Rosamond, for your shared passion on the subject. Denise Klempay, BS Zoology Kent State University.


About News

Moonshine Ink brings you Tahoe news straight from the source. Our team of hardworking journalists uncovers North Tahoe and Truckee news stories with in-depth reporting and our authentic “for the community, by the community” spirit.

In our “On the Spot” section you’ll find the facts on everything from politics to the environment to local business. We’re your Tahoe newspaper, delivering stories you can trust.

Subscribe to the feed

Latest Tweets @moonshineink

  • A bridge over the mouth of Emerald Bay? 3 days 16 hours ago
  • The closing of T Pots in Truckee. 4 days 15 hours ago
  • RT @snowguy530: Lunar eclipse over Donner Summit. #Truckee #eclipse 4 days 17 hours ago

Look for the latest Moonshine Ink issue on newsstands now.

Look for the latest issue in newsstands now.

Or subscribe and enjoy it hot off the press in your mailbox.

April 11, 2014