As infestations worsen, property owners test innovative weapons to keep lagoons clear

By Tom Lotshaw/Tahoe Regional Planning Agency

The Tahoe Keys Property Owners Association (TKPOA) is working on multiple fronts to combat the harmful aquatic invasive species in its canals and lagoons—plants like Eurasian watermilfoil and curlyleaf pondweed, and the non-native bullfrogs and warm water fish that can follow their spread.

“These aquatic invasive plants are a problem throughout Lake Tahoe, cover most of the Tahoe Keys, and it’s getting worse every year,” said Andrew Kopania, chair of the Tahoe Keys Water Quality Committee, a subgroup of the Board of Directors.

“They’re a threat to Lake Tahoe’s environment, recreation, and economy,” Kopania added. “We need to continue to act to address that threat, using the best science, collaborating with stakeholders, and implementing effective controls.”

No one knows how Eurasian watermilfoil and curlyleaf pondweed first arrived in Lake Tahoe and the Tahoe Keys, but they were most likely transported to the lake by a boat or a dumped fish aquarium.

Eurasian watermilfoil was first found in Lake Tahoe in the 1970s. Curlyleaf pondweed—potentially a larger threat because of its ability to live in colder open water—was first identified in the Tahoe Keys in 2003. The aquatic invasive plants found an immediately suitable habitat in the shallow, warm waters of the Tahoe Keys.

TKPOA has tried to manage the infestation for recreation purposes through manual harvesting since 1984, spending as much as $400,000 a year. However, while harvesting the dense mats of the plants helps to clear the channels temporarily, resulting plant fragments increase the growth and spread of the population.

A crew rakes up aquatic weeds to clear the way for boat traffic. Photo: Tahoe Keys Property Owners Association

A 2009 survey of the Tahoe Keys found approximately 70 percent of its 172 acres of lagoons infested. And in the last five years, it is estimated that curlyleaf pondweed coverage has increased up to 35 percent. Today, more than 90 percent of the Tahoe Keys is infested.

For several years, TKPOA has been working with TRPA, Tahoe Resource Conservation District, and Lahontan Regional Water Quality Control Board to develop a comprehensive management plan with strategies to address the invasive species.

TKPOA has researched methods and consulted with a wide range of scientific experts from around the country to fight aquatic invasive species.

The weed-harvesting program in the Tahoe Keys is now picking up four times as many plant fragments as before. This is important because small fragments of the plants can easily break away and start new infestations in other locations.

TKPOA has installed a boat back-up station near the Tahoe Keys entrance to Lake Tahoe, where boat operators are asked to stop and put their boat in reverse to remove any weed fragments that may be attached to the propeller to keep them from being carried into the lake.

Changes are also being made on land. TKPOA has put in place new landscaping and irrigation rules to reduce stormwater pollution and keep nutrients like phosphorus and nitrogen out of the canals and lagoons where they can fuel plant growth.

Harvesting Eurasian watermilfoil and curlyleaf pondweed has helped keep boat channels open in the Tahoe Keys, but the weeds have spread and approximately 70 percent of the 172 acres of lagoons are infested.

TKPOA is also working with partner agencies on test projects to identify new methods to control aquatic invasive species.

The neighborhood is testing a “bubble curtain” between its lagoons and Lake Tahoe to see if it can keep weed fragments from spreading into the lake. It wants to test laminar flow technologies in 7 to 8 acres of the canals and lagoons to see if increased oxygenation of the water can help stop the recurrence of aquatic invasive plants and reduce conditions that promote their growth.

Among the treatment options, there are no easy solutions in the Keys. In response, TKPOA, TRPA, and Lahontan are working to launch a broad collaborative process and environmental analysis to review the Tahoe Keys management plan—including one of its most controversial aspects, a TKPOA proposal to test the use of aquatic herbicides in a portion of its canals and lagoons as one way to knock down the populations of invasive plants.

The federally approved herbicides are just one aspect of the Tahoe Keys multi-faceted management plan and would be used only temporarily and in conjunction with other control methods. Under the proposal, the herbicides would be used in the most infested areas to reduce the population to a level that can be controlled through other methods. The herbicides are used in other lakes across the country to selectively target invasive species like Eurasian watermilfoil and curlyleaf pondweed, but have never been used in Lake Tahoe or any other federally designated Outstanding National Resource Water with the highest level of protection, as is the case with Lake Tahoe.

The proposal has raised concern among some residents and groups like the Tahoe Water Suppliers Association.

“The Tahoe Keys is showing real leadership in working to address the invasive species in its waters,” said Dennis Zabaglo, aquatic resources program manager for TRPA.

“Working together to find an acceptable collaborative solution for the Keys is the most important opportunity we have to control far more serious spread and infestation lake wide. Success is our only option and working together is the path to success,” said Joanne S. Marchetta, executive director at TRPA.

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