LAKE COUNTY, Calif. – Local officials this week addressed concerns about whether it’s safe to swim in Clear Lake due to aquatic weed abatement practices and a widespread cyanobacteria bloom that’s developed over the past month.

Lake County Water Resources Director Phil Moy was one of the county staffers who responded to those two concerns from community members.

The issue of herbicide use to control nuisance aquatic vegetation has been raised over the past few weeks after a notice that was sent to Habematolel Pomo tribal members was circulated on social media.

County Water Resources staffer Carolyn Ruttan said she sent out a letter to tribe as part of a state requirement to notify all public agencies of any activity on Clear Lake. In this case, she was announcing the start of the summer aquatic weed abatement activities.

Linda Rosas, Habematolel’s environmental director, in turn sent out a notice via mail earlier this month to tribal members, advising against swimming in Clear Lake due to the planned herbicide use.

“It was an internal document, and it was an advisory not a warning,” said Rosas.

Copies of Rosas’ notice and Ruttan’s letter were then circulated on social media, resulting in community members questioning if it was safe to swim and pursue other recreational activities on the lake.

Rosas, who is fairly new to the job, said she doesn’t know a lot about herbicides and pesticides, so when she received the notice about the county’s program, she decided she should err on the side of caution and notify tribal members.

She said she was concerned that if anything happened to a tribal member swimming in the lake, she could be negligent for having not released the information. “That’s a big responsibility.”

Rosas said the advisory notice went out to the general tribal membership in a regular mailer. “It just somehow blew up and got out of control, when it was not really meant to be shared.”

Ruttan said Water Resources has received a lot of calls due to the notice, and so she and Rosas met on Thursday so she could explain the county’s aquatic weed abatement program.

“I need answers to all my questions,” said Rosas, who plans to relay the discussion to tribal members.

Moy said that, from the county’s perspective and based on the environmental documentation prepared for the aquatic weed control program, the herbicides do not adversely affect the water for swimming. 

“Tribal environmental offices may differ in their opinion of the program, but the county’s position is that the areas treated with the herbicides are safe for swimming,” he said.

Ruttan added that herbicides and pesticides are well regulated at the local, state and federal level, and tested extensively by federal and state agencies. She said stringent requirements are placed on their use.

She said only one herbicide that the county uses for its program, 2,4-D, requires a 24-hour notice be issued against swimming. So far it hasn’t been used this season although it will be later on, she said.

Ruttan said that herbicide is used to protect swim beaches so weeds don’t become a hazard for the swimmers. There have been issues with children and other swimmers getting tangled in the weeds, she added.

Ruttan said 2,4-D is used on Eurasian watermilfoil, the worst weed – besides hydrilla, which the state deals with – in Clear Lake. It’s not even a habitat for fish. She said it’s all over Clear Lake, and is known to be a problem elsewhere..

“It’s now Washington state’s most noxious weed,” with that state running a program to eradicate it, she said.

Cyanobacteria bloom impacting lake

Moy said the other factor currently affecting the lake is a widespread cyanobacteria bloom.

Ruttan said the bloom began to appear around the middle of May. 

She said cyanobacteria – a primitive life form – splits every four hours, thus doubling in number. This year it is very aggressive in the lake; she said she’s not seen so much of it before.

Sarah Ryan, environmental director for Big Valley Rancheria, explained that cyanobacteria is natural part of the ecosystem that studies have shown can come to dominate a water system when there are excessive amounts of phosphorous or nitrogen.

This year it looks very different – it appears in shades of near-fluorescent green or bright blue – and is collecting on the surface.

Over the last several years, microcystis was the prevalent kind of cyanobacteria on the lake, Ryan said.

However, this year, dolichospermum is the chief type of cyanobacteria in Clear Lake this year; it also appeared last year. Ryan said the same cyanobacteria also has been detected in Blue Lakes this year.

As dense as the surface coverage of the cyanobacteria is in Clear Lake is this, Moy said no toxins have been detected in it so far. 

He added that monitoring is continuing as the situation could change. 

Ryan also reported that water samples taken from several sites, in particular areas where the cyanobacteria bloom looked particularly bad have, in previous testing conducted his season, showed no toxins. 

However, on Friday she said a recent set of samples may have some low toxin levels, and the tribe is awaiting lab results to be completed early next week.

As a precaution, Moy said swimmers are advised not to consume raw lake water and dog owners should likewise restrain their pets from consuming or coming into contact with lake water as the dog may lick its fur. Swimmers should rinse off soon after getting out of the water.

Separately, Dr. Karen M. Tait, Lake County’s public health officer, told Lake County News that she’s also recommending caution when swimming for both pets and people, particularly in areas where water does not appear normal.

Tait said one “suspect” case of gastrointestinal illness associated with swimming in the lower arm of Clear Lake has been reported to her office. That case involved symptoms that manifested within a few hours of swimming and lasted for a couple of days.

However, Tait cautioned that there is no way to prove the connection between swimming and the illness as other causes weren’t ruled out. As a result, she’s considering it suspect for surveillance purposes, adding she will be watchful for any additional cases.    

Updates on the cyanobacteria blooms in California can be found at www.mywaterquality.ca.gov/habs/index.html .

For more information contact the Lake County Water Resources Department at 707-263-2344.

Email Elizabeth Larson at This email address is being protected from spambots. You need JavaScript enabled to view it. . Follow her on Twitter, @ERLarson, or Lake County News, @LakeCoNews.