Study could guide herbicide use in the Tahoe Keys

A proposed study this summer could be a significant step in getting rid of Lake Tahoe's weed problem.

During a proposed "dye tracer" study by the U.S. Department of Agriculture, researchers would use a fluorescent dye to look at how an herbicide would travel after being applied to water in the Tahoe Keys.

Although not yet permitted, herbicide use could become an important tool to control infestations of Curlyleaf pondweed and Eurasian watermilfoil at Lake Tahoe, said Lars Anderson, the lead researcher on the proposed study.

The aquatic plants have infested nine marinas and more than 15 acres of shorezone areas in the past 20 years, according to Lahontan Regional Water Quality Control Board documents.

The proposed dye tracer study will be reviewed by the Water Board at their regular meeting on Wednesday.

Current methods to harvest milfoil and pondweed in the Tahoe Keys each year keep the plants from inhibiting boat travel. But harvesting isn't a permanent solution and creates plant fragments that spread the weeds around the lake.

"It's like mowing the law, you have to do it continuously," Anderson said.

The Water Board's current code essentially prohibits herbicide application to water by requiring pesticide concentrations to not exceed the lowest detectable levels, but water board staff are developing rule changes that could allow application under certain circumstances, such as protecting public health or eliminating invasive species.

The amendment could come before the Water Board for consideration as soon as November, said Dan Sussman, an environmental scientist with the agency.

If approved, this summer's study would include a late spring and late summer application of dye to the Tahoe Keys, Anderson said.

Because low concentrations will be used, Anderson said he does not expect the study will be highly visible. Researchers will use fluorometers to measure where and, in what concentrations the dye ends up in the Keys.

A presentation on the dye tracer study is the first item on the Water Board's April 14 meeting agenda. The meeting begins at 3 p.m. in the Lake Tahoe Community College Board Room at One College Drive in South Lake Tahoe.

Also at Wednesday's meeting:

• The Water Board will consider requesting funds from the State Water Board Cleanup to expand an Asian Clam eradication pilot project to Emerald Bay. Divers delineated the extent of the clams, which excrete nutrients contributing to algae blooms and litter the bottom of the lake with shells, in Emerald Bay in August 2009.

The expanded pilot project, as well as an in-depth survey of the clam population in the bay, will cost $588,720.

Results from a 2009 pilot project to remove Asian clams from portions of the southeast part of Lake Tahoe are expected in late spring 2010.

• The Water Board will consider whether to adopt an National Pollutant Discharge Elimination System permit regulating the California Department of Fish and Game's application of rotenone to eradicate introduced fish species, including Rainbow trout, from portions of the Silver King Creek and its tributaries near Markleeville.

The pesticide application would be used as part of Paiute Cutthroat Trout recovery efforts. The fish is one of the rarest subspecies of trout in North America, indigenous only to the Silver King Creek watershed.

The Water Board has allowed the conditional use of rotenone for specific fisheries management activities since 1990.

Discussion on the proposed Silver King Creek and Asian clam projects is scheduled for after 7 p.m. Wednesday in the Lake Tahoe Community College Board Room at One College Drive in South Lake Tahoe.