With Emerald Bay cleaned up, attention turns to other infestations

By Brenna Blessing/Tahoe Resource Conservation District

Eurasian watermilfoil and curlyleaf pondweed are two of the most widespread and problematic aquatic invasive species in Lake Tahoe.

The weeds grow aggressively and are easily spread, producing fragments and clones that can float, sprout roots, lie dormant through winter, and start new satellite populations. But their populations can be controlled, and more than 40 public, private, and nonprofit partners in the Lake Tahoe Aquatic Invasive Species Program are working to do just that.

One example of that work is Emerald Bay, where several Eurasian watermilfoil plants were first observed in 2000. By 2003, the plants had infested nearly an acre of the bay, choking out the clear water and sandy beaches at one of Tahoe’s most iconic and heavily visited locations.

A diver suctions up Eurasian watermilfoil from the bottom of Lake Tahoe. Photo: Monique Rydel, © Marine Taxonomic Services, Ltd.

The aquatic invasive species partnership assessed the Emerald Bay infestation and started testing various control methods using combinations of bottom barrier mats to deprive the plants of sunlight and diver-assisted suction removal. Action became imperative as the invasive plants continued to spread, covering 3 acres of the bay’s shoreline by 2008 and 6 acres by 2010.

Partners joined forces for an extensive, multiple-year project to control the infestation starting in 2010. The weeds were successfully eliminated in Emerald Bay over several years and the bay remains weed-free nearly five years later.

Partners are now working to replicate that success around the lake, following a three- to five-year control strategy provided by an aquatic invasive species implementation plan prepared by researchers at the University of Nevada, Reno.

“The plan uses an ecological and science-based framework to prioritize sites for treatment and calls for controlling satellite populations to achieve containment,” said Nicole Cartwright, executive director of the Tahoe Resource Conservation District.

Since 2005, partners in the Lake Tahoe Aquatic Invasive Species Program have implemented control projects and removed more than 32,000 gallons of aquatic invasive plant biomass from the lake and its tributaries.

Bottom barriers have been used to treat over 520,000 square feet of the lake and over 770,000 square feet of infestations have been treated with diver-assisted suction removal. Through 2017, approximately 36 acres of Lake Tahoe and the Truckee River have been treated and inventoried by program partners.

With Lake Tahoe’s boat inspection program successfully preventing new introductions of aquatic invasive species, partners are working to ramp up these types of control projects to better manage, if not eradicate, harmful invasive species like Eurasian watermilfoil and curlyleaf pondweed to keep them from spreading.

This work will continue for years to come, as continuing experiments with new treatment methods are tested, such as ultraviolet light, which has proven in lab studies and small field tests to damage the DNA and cellular structure of aquatic plants. Tahoe Resource Conservation District is working with partners on post-treatment monitoring to determine how effective an ultraviolet light pilot project was at Lakeside Beach and Marina with plans to release the final results in early 2019.

Other projects to treat and monitor these aquatic invasive plants in 2018 include surveillance monitoring in Fleur du Lac and Tahoe Vista, with the potential for a second round of treatment if needed; treatment in the Truckee River reaching downstream; post-treatment monitoring at Crystal Shores; and treatment at Elk Point Marina, where the Elk Point Country Club Homeowner’s Association is working with Nevada Division of State Lands and contributing a quarter of the project’s cost.

Lake Tahoe’s aquatic invasive species control program is also seeing a boost with additional funding from federal partners, including $1 million from the U.S. Army Corps of Engineers and $3.1 million appropriated by Congress as part of the Lake Tahoe Restoration Act.

“Prevention, early detection, and control programs are the best defenses against aquatic invasive species at Lake Tahoe and offer the best hope for successful management of aquatic invasive plant infestations,” said Dennis Zabaglo, aquatic resources program manager for TRPA.

“Although aquatic invasive plants can be difficult and costly to control once they are widely established, our strategy for Lake Tahoe has shown we can control these infestations.”

Brenna Blessing is the outreach specialist at Tahoe Resource Conservation District.