LAKE COUNTY, Calif. – One of the signs of summertime is the appearance of lake weeds, which county officials are working to address in order to keep the lake's recreation opportunities open and accessible.
The county of Lake reported Monday that Water Resources staff went into action last week as the signs of the seasonal algae bloom began to emerge on Clear Lake.
Water Resources staff is implementing the department’s multipronged approach designed to help minimize the impact of the algae, working with specialized contractors to treat the blue-green algae, according to the county's report.
It's a big job: Clear Lake is the largest natural freshwater lake within the boundaries of California, and at an estimated two million years old, it also is one of the oldest lakes in North America, and a popular spot for summertime activities on the water, from kayaking and waterskiing to sailing and fishing.
Clear Lake has more than 68 square miles of surface area and 100 miles of shoreline, with numerous channels and bays, and a large drainage basin.
It's “eutrophic,” which means it's rich in nutrients that support the growth of algae and aquatic plants, which in turn, supports large populations of fish and wildlife. That, coupled with its warm, shallow depth, gives rise to the summertime weed issues that, while a natural part of the lake, can create headaches for residents and visitors alike.
The algae mitigation efforts now under way are part of a focused county approach funded by a $1.4 million appropriation by the Lake County’s Board of Supervisors to protect Clear Lake’s ecosystem and to enable residents and visitors to enjoy the lake to the fullest extent possible this summer, the county said.
Several species of blue-green “algae” – also known as cyanobacteria – are present in Clear Lake, but the predominant species in this year’s bloom is Lyngbya, the county reported.
Lyngbya has become more prevalent on the lake in the last few years. The county said the sunlight's ultraviolet rays kill the blue-green algae cells, which then produce an extremely foul odor and create floating mats that turn turquoise, purple, orange and yellow.
The Monday report noted that the recent algal bloom was noticeable in “limited” areas such as Redbud, Austin and Highlands parks in the city of Clearlake and Island Park in Clearlake Oaks, and that “the vast majority of the lake is not impacted.”
However, Lake County News readers have reported seeing algae blooms in other areas as well, including the areas offshore of Lakeside County Park outside of Lakeport.
Reader Sharon Thornton posted pictures on the Lake County News Facebook page over the weekend showing what appeared to be thick algae mats coating the top of the lake near the park.
A drive past the Rodman Slough in recent days also has revealed thick mats on the surface of the water there.
Public Works Director Scott De Leon, who also oversees Water Resources, said the county isn't taking any measures to address the algae in those areas, where he said Mother Nature typically deals with the algae.
He said what people may be seeing in those areas is aquatic weeds that have surfaced, rather than an actual algal bloom.
County staff has established boat lanes at both sites in order to make the lake accessible to boaters, he said.
De Leon said the county is looking to roll out more aggressive algae mitigation in the south county area, near Clearlake Oaks and Clearlake, said De Leon.
“Those are the areas that are historically impacted and that's where we're focusing our efforts,” he said.
De Leon said that while the county is looking at mechanical harvesting – including a technique that would essentially vacuum the algae mats and, through the use of a centrifuge, dewater the material, perhaps making it possible to dispose of only the algae material – that process isn't being used right now.
He said some mechanical harvesting contractors had been set to work parts of the lake. However, he added that in the areas where they were assigned to work the weeds “haven't really got going like they were last summer.”
The slower weed growth could be a function of the cooler, early part of the summer and the late rains, explained De Leon.
The late rains and winds kept the lake stirred up, so it's not as clear as it was last year, he said.
In some areas along the west shore of Lakeport, where weeds were showing up in abundance, De Leon said a weed spray program seems to be yielding positive results.
Other mitigation efforts include assisting citizens and resort owners with the installation of pumps to provide aeration and circulation by spraying water onto the surface of algae mats that can help to knock down the algae around private docks and beaches, De Leon said.
Lake County Health Officer Dr. Karen Tait and officials from the county’s Environmental Health Division together once again recommended that people and pets stay out of areas of the water where visible algae mats or scum are present and reemphasized that untreated lake water should never be used for drinking.
Lake County Health Department officials have posted advisory signs at the impacted public beaches and continue to respond to calls and e-mails from concerned members of the public.
“Last year, despite heavy blooms in some locations, measured toxin levels had been within safe recreational water levels,” said Tait. “I am hopeful this will be the case again this year.”
Tait indicated that the mix of algae types and extent of production can fluctuate and tests are not available for all possible toxin types.
Based on research being done on the lake water, only minimal and mostly no measurable toxins have been detected, the county reported.
For more information about the algae bloom and efforts to mitigate its impacts, contact the Lake County Department of Water Resources at 707-263-2344.
For health-related questions, contact the Lake County Health Services office at 707-263-1164.
E-mail Elizabeth Larson at
How to resolve AdBlock issue? 
