Tahoe RCD takes on invasive weeds with innovative UV technology

Most California residents are familiar with the phrase “Keep Tahoe Blue” and historic efforts to protect Lake Tahoe from sedimentation and pollution. One lesser known threat to Lake Tahoe’s beauty and recreational value is invasive species, particularly the eurasian watermilfoil and curlyleaf pondweed. Both species of aquatic invasive plants reduce Lake Tahoe’s water quality and clarity, compete with native species, hinder boat navigation, and create an “unnatural habitat” for other non-natives to flourish. Over the last few years, the Tahoe Resource Conservation District (RCD) has been exploring a way to control this weed through germicidal ultraviolet (UV-C) light, and findings have been promising.

Eradicating a weed underwater is not easy. Lake Tahoe is currently in a Basin Area Plan that does not allow the use of aquatic herbicides, which leaves the RCD two approved methods—hand pulling and using bottom barriers. Hand pulling requires trained divers to swim to the lake bed and pull weeds, feeding them into a suction vacuum as they go. Divers who also happen to have a background in biology are few and far between, and typically consist of a small niche in the research field. The second technique uses bottom barriers secured to the lakebed with rebar and sandbags, and prevents light from nourishing the invasive plants underneath. Both methods are effective, but are also labor intensive, require specialized training, and carry a safety risk. The RCD was already interested in expanding their toolbox for controlling the aquatic weed when they heard a pitch for the UV-C pilot program from the start-up Inventive Resources.

Thick bottom barriers block sunlight and are an effective way to control invasive aquatic plants

Contrasted with hand-pulling and using bottom barriers, one technician can operate the UV-C light from inside the boat without ever getting in the water, and much more quickly, making this a significantly more sustainable option for treating weeds in Lake Tahoe. The craft is simple, a small pontoon boat with middle cut out to make room for the UV shining apparatus. UV-C lights are attached to a treatment apparatus that can raise and lower, with a top and 4-inch side walls to direct the light inside. There are fish deterrents to evacuate the treatment area before the light is used.

In total, over 40 partners are involved in the larger aquatic invasive species program, which includes boat inspections, early detection and monitoring, and more control projects. The initiative is being funded by Lake Tahoe Science and Lake Improvement Account grant from the California Tahoe Conservancy and by private contributions from the Tahoe Fund.

Tahoe RCD’s District Manager, Nicole Cartwright, has been able to witness the community’s awareness towards invasive species increase over time. Over the last decade or so of implementing their Aquatic Invasive Species control program, they have had one-on-one interactions with the public through boat inspections and workshops, and they are meeting more people who are already knowledgeable about invasive species and their impact on the lake.

Invasive species, which are spreading throughout many of California’s ecosystems, are by nature hardy and hard to get rid of once they gain a foothold. Controlling them requires persistence, science-based research, and successful programs that are as adaptive as the weeds themselves. Keep track of Tahoe RCD’s UV-C pilot program and their other work through their Facebook page.