Reopening of parts of the Tahoe Keys delayed due to herbicide level

SOUTH LAKE TAHOE, Calif. - The three-year-long Control Methods Test (CMT) began this summer in the Tahoe Keys. The projected mid-July reopening date of closed waterways has come and gone and it may be several more weeks until boaters, paddlers, swimmers, and pets can access those closed areas.

The reason for the delay is the need for the double turbidity curtains to stay in place for waterways treated with herbicides. Per their permit with Lahontan Water Board, the Tahoe Keys Property Owners Association (TKPOA) and those hired to do the tests cannot remove the curtains until all herbicide residues from Triclopyr get below 1 part per billion. It is currently hovering around 3 parts per billion according to the TKPOA interim General Manager Mark Madison.

The curtains confine the herbicide applications and ensure the herbicide residues do not migrate towards the West Channel, which connects the West Lagoon to lake Tahoe.

What they are also doing is preventing the normal water motion that comes from motorized and non-motorized boats moving through the Keys. Due to the extension of time for the curtains to be in place and restricted boating use, water has become stagnant and there are higher algae levels.

The approved CMT in the Tahoe Keys waterways is on aquatic invasive species (AIS) in an attempt to eradicate them from Lake Tahoe. The Tahoe Keys are ground zero for the infestation of aquatic invasive weeds in the Basin, which has spread beyond the Keys’ shallow lagoons, infecting more than 100 acres of the Lake itself.

The Control Methods Test (CMT) was unanimously passed by the Lahontan Regional Water Quality Control Board and the Tahoe Regional Planning Agency Board and is supported by the League To Save Lake Tahoe. They used stand-alone and combined use of various approaches including targeted herbicides and UV-C light to reduce and control the abundant growth of invasive and nuisance aquatic weeds in the Tahoe Keys west lagoon and Lake Tallac areas.

Madison said the CMT is a long-term endeavor to try and remove the weeds. The chemicals and ultra-violet light tests are done, and thousands of test points throughout the keys will monitor the results for three years. If successful, the testing could possibly move to other areas of Lake Tahoe.

"Despite the problems and challenges, this control methods test is vital for the long term," said Madison.

"We are encouraging people who are suffering to just be patient," said Madison. "This information is just so important."

In the map above, the test areas are marked A, B, and C. The curtains on the southeastern side, B, should be able to be removed soon, Madison said. A is the area struggling with the Triclopyr levels. The areas on the map without color are those where the testing did not occur this year.

Many people have been concerned with the algal blooms seen in the closed waterways, but Madison said they look bad and are a nuisance, but it's due to the stagnant water combined with the current drought and warm temperatures.

Madison said the permit says the Triclopyr needs to be below 1 part per billion, which is one drop of water in a normal size swimming pool. He said this low amount is very unusual and four hundred times lower than one would expect to see in a permit.

The TKPOA is looking at possible mitigation efforts. They could spend more than the $3 million project is already costing them, or let nature run its course.

"People are working on this and trying to do everything they can with a tough situation," said Madison.