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.


But those messages did not make it into the mainstream. Following the 2008 research and 2009 publication of the report, media and press release material portrayed Lake Tahoe as susceptible to widespread mussel invasion.

Statements like this one, posted on the University of Nevada, Reno website under the headline “Researcher Finds Quagga Mussel Can Survive In Tahoe” were common: “If established, the mussels could forever alter the lake’s sensitive ecology; they could clog water intakes, encrust boats and docks, and cover now-pristine beaches with sharp and reeking shells.”

By the time the message made it to the media, the picture of Lake Tahoe’s mussel threat became even more distorted. An August 2009 San Jose Mercury News article led off: Scientists say a new study shows invasive quagga mussels can survive and possibly reproduce in Lake Tahoe.

“This could potentially be catastrophic for the lake,” said Ted Thayer, natural resource and science team leader for the Tahoe Regional Planning Agency.

Despite the ambiguous results, limited scope, and short timeframe of the study, Chandra’s 2009 risk assessment has been the lone, local science on the quagga mussel survival matter for the last four years.

“It is scientifically unconscionable that an inconclusive, four-year-old laboratory study that did not meet minimum comparative or scalability standards should justify spending millions to prevent an extremely unlikely problem from occurring,” wrote Urie.

And that is not the only limited, short-term report that Chandra had published on local invasive species threats. Chandra was one of the authors of a 2011 report on the ability of the New Zealand mudsnail to survive in the Truckee River watershed and Lake Tahoe.

That experiment only lasted two weeks, even though the study’s own introduction stated, “The ability of [New Zealand mudsnails] to survive for up to three weeks out of water contribute to the species’ ability to expand its range.”

Later on the report said: “Ideally, the experiment would have occurred over more than 14 days, but the need for immediate information to assist with ongoing management decisions as well as funding limitations necessitated the short duration of the experiments. In fact, results from this, as well as other studies in the region, led to the establishment of new guidelines for boat permitting and inspection at Lake Tahoe to proactively reduce the likelihood of nuisance aquatic species introductions.”

When questioned about why further study of the mussel risk was not completed, Chandra said that until now funding was not available to complete studies on the mussel’s full life cycle in Lake Tahoe, or to conduct an experiment that included more than one site, or lasted more than 51 days.

That has now changed. Chandra and a team of researchers were recently funded to complete a more in-depth study this summer, and results should be released this fall. The study will last between 120 and 160 days, Chandra said. It will use water from the Cave Rock area as well as the Tahoe Keys. And it will study the entire life cycle of the animals.

If it were not for the more than 500 hours of intense scientific research that Truckee resident Steve Urie has conducted over the past several months, all watercraft entering Donner Lake would likely have to undergo mandatory inspections, and each boat would have been charged a boat inspection fee this summer.

Urie, a retired businessman with a degree in civil engineering, was intimately familiar with Donner Lake, having lived on the lake for 30 of the 40 years he has been a local resident.

His interest in invasive species was first sparked when he heard California Sen. Dianne Feinstein say in a speech at the 2010 Lake Tahoe Summit: “If you organized all the Asian clams currently in the lake end to end, it would stretch 3.5 miles long.”

Being an engineer, Urie began calculating how many clams it would take to organize a single-file line of clams 3.5 miles long, and concluded that quantity of clams would likely fit into the back of a pickup truck.

“It just did not make sense to me. The reports that came out were so exaggerated,” said Urie.
The more Urie investigated the issue, the more intrigued he became. He read dozens of studies and reports on the calcium requirements of mussels, conversed with experts across the state, and researched years of Tahoe and Donner Lake water studies.

After the equivalent of more than two months of full-time research, he delivered a seven-page, sourced position paper to the Town of Truckee. Urie’s stance was summed up in one of the last sentences of the paper: “No legitimate AIS [aquatic invasive species] threats to Donner Lake have been identified, and until one is, it is illogical and impractical to implement a needless fee-based program that inconveniences residents and visitors alike.”

After an April Town of Truckee invasive species working group meeting where Urie and Chandra had a spirited debate over the topic, the Town of Truckee decided to recommend that the mandatory boat inspection ordinance not be enforced this summer, and that voluntary inspections continue.

“It was the right result. It is exactly what they should have done,” said Urie. “If they had taken off with this, we would have had a boat inspection program at Donner Lake forever. It is one of those government programs that once it gets going, you can never pry it away from them.”
One of the issues the Town of Truckee faced was that the ordinance they passed specifically identified mussels as the invasive species that was being targeted, and declared that the mussels were an “imminent” threat.

“There is obviously not a significant or imminent threat,” said Dan Olsen, the Town of Truckee’s animal services and code compliance manager, following the decision by the town to not recommend mandatory inspections this summer.

Chandra emphasizes that while zebra and quagga mussels have made all the headlines, “it is not all about the mussel. If we make this just about mussels, we are in very deep trouble.”

Chandra lists a number of invasive threats to the region, including curlyleaf pondweed, Brazilian elodea and hydrilla. Curlyleaf pondweed is already growing in Lake Tahoe.

But Urie says that Donner Lake and the reservoirs in the area would be unlikely targets for an invasion of these plants. The annual fluctuations of the water bodies’ levels exposes bare ground along a significant portion of the shoreline to freezing temperatures, greatly reducing the risk of large-scale exotic plant invasions.

And many of the invasive species that can impact an ecosystem — creatures like Asian clams and crawdads — have already established in Donner Lake.


But Chandra is essentially erring on the side of caution. With inconclusive and incomplete science on invasive species, he said his approach has been to “be protective first, and back away from protection later.”

“We actually don’t have a handle on these species and the plasticity of them,” said Chandra, noting that more research is needed for the science to be able to more accurately pinpoint invasive species threats.

“That is unfortunately how the science has not caught up,” he said. “We have not caught up to tell you, plant-by-plant, what might invade an area.”

Donner Lake and other local lakes have long been exposed to invasive species. And even today, the voluntary inspections are a patchwork that leaves hundreds of boats to launch uninspected in local waters each year. 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.

Even at local reservoirs, boaters can simply drive to the edge of the lake off of a dirt road and back an uninspected boat into the water.

“There is no way to control that unless you shut off access to the lake,” said Truckee Animal Control Manager Olsen.

So far, the costs of the voluntary inspections have been borne by the Truckee River Fund, a group supported by the Truckee Meadows Water Authority, which has given the Tahoe Resource Conservation District nearly $1 million over the last four years to conduct boat inspections. That funding is dwindling, and the Tahoe Resource Conservation District was expecting inspection fee revenue to begin to pay for some of the costs beginning this summer.

Tahoe pays nearly $1.5 million a year to run its boat inspection program. Only about half the program is funded by fees; the other half comes from public money.

In Truckee, Urie believes that putting the mandatory inspection on hold as the science and risk is evaluated is the proper procedure. At the final invasive species working group meeting, Urie asked about a Donner Lake risk assessment noted by one presenter. When he was told the risk assessment was not published, and later told that the risk assessment was simply notes from meetings and presentations that had not even been compiled into a complete document, he wondered how a program could be put in place.

“You are asking the Town of Truckee to put in place pretty invasive procedures, and you are basing it on a risk assessment that has not been published?” he asked. “I think there is some real dereliction to ask to put in place a program that there are no facts to support.”

The Town of Truckee and the Tahoe Resource Conservation District say they are willing to re-examine the science behind the program.

“I am not opposed to this discussion happening right now,” said Kim Boyd, the assistant district manager with the Tahoe Resource Conservation District. “I think this is a great time to have this discussion and really evaluate the risks.”

But Brian Hanley, a local boater, said he thinks that if Urie had not spent 500 hours investigating the science behind invasive species, the outcome of the boat inspection program process would have been much different.

“I think if Steve [Urie] had not been there, the science may have been ignored,” said Hanley.

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  • David Bunker

    David Bunker almost dropped out of journalism school to hunt non-native rats on an uninhabited Pacific island. Instead, he graduated college and launched into a career of dump truck driving and ditch digging before taking up writing as a profession. He’s written for newspapers and magazines across the West and won numerous first place awards in the California and Nevada press associations.

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