Sun-blocking barriers helping fight invasive weeds in Lake Tahoe lagoon

The invasive species include Eurasian water milfoil.

SOUTH LAKE TAHOE, Calif. — Scuba divers have installed more than 100 sun-blocking barriers on the bottom of a lagoon on the south end of Lake Tahoe to try to help stunt the growth of invasive aquatic plants that have taken over the man-made waterways in the Tahoe Keys, a community of more than 1,000 homes next to the canals.

They will remain in place no later than Oct. 15, but will be put back again during the warmer months for the next two years. Homeowners have been using the barriers in a smaller capacity for the past two years, but the recent installation is the largest use of the barriers in the community.

The installations are the beginning of the Tahoe Keys Property Owners Association’s multi-year plan to wipe out the plants, the Tahoe Daily Tribune reported this week.

“2015 is when everything really took off and we started to try and control everything,” said Greg Hoover, association water quality manager and aquatic invasive species management coordinator. “There were spurts in the past where we’ve incorporated science into this, but in 2015 we brought in a consultant agency and a scientist that has a Ph.D. in aquatic plants.”

The association has $2.4 million put aside to run its eradication program, with the possibility of more funding coming through grants. The plan also envisions small-scale testing of herbicides.

A decision by the U.S. Environmental Protection Agency in September 2015 determined that some herbicides may be approved for use on a case-by-case basis in Lake Tahoe. So in January, the association applied for a permit to test low levels of three herbicides at nine test sites in 2018. The test sites would cover about 8 percent of the Keys and would be in dead-end lagoons far from the lake.

If the permit is approved and the results are promising, herbicides could be used as a method for weed eradication in the Keys starting in 2020, Hoover said.

The test sites would have multiple surface-to-bottom barriers to ensure the herbicides, which are considered nontoxic to humans, fish and wildlife, would not reach the lake, the association stated.

The Tahoe Keys was created in the late 1950s by dredging an estimated 5 million cubic yards of material from the marsh at the mouth of the Upper Truckee River.

The effort destroyed much of the river’s marsh, a major filtration system from Lake Tahoe’s largest tributary.

The resulting 172 acres of warmer, calmer lagoons became prime habitat for aquatic invasive plants like Eurasian milfoil and curly-leaf pondweed. They now cover more than 90 percent of the channels.

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