LAKE COUNTY, Calif. – The Lake County Water Resources Department has issued an update on Clear Lake’s conditions, which include continuing cyanobacteria blooms and fish die-offs.

The agency reported that Clear Lake is suffering the effects of a second fish kill, this time off the shores of Lakeport.

This latest fish die-off is most likely the consequence of nutrients, cyanobacteria and warm water temperatures adversely affecting water quality, primarily dissolved oxygen, officials said.

Just like people, fish rely on oxygen to breathe and process nutrients in their bodies. Warm water fish such as those living in Clear Lake need to have about 5 parts per million, or ppm, dissolved oxygen to thrive.

Water Resources said that, like many other lakes in California, nationwide and around the world, Clear Lake has this summer been host to a large, dense, persistent cyanobacteria bloom. Cyanobacteria is sometimes called blue-green algae.

The bloom has been lakewide with various intensities due to wind, water depth and nutrient cycling, specifically, phosphorus. Officials said these dense blooms produce ample oxygen during the day, but consume oxygen during the dark hours at night.

The very warm water conditions also contribute to the problem because warm water holds less dissolved gases – including oxygen – than cold water but warm water also increases the fishs’ metabolic rate. So the fish need more oxygen to digest and thrive, but the water cannot hold as much oxygen as it can in the spring, winter and fall months, according to the report.

At the current water temperatures of Clear Lake – which are ranging between 80 and 84 degrees Fahrenheit – the dissolved oxygen saturation point is about 7.9 ppm. Recent monitoring by the California Department of Food and Agriculture has shown the dissolved oxygen concentration off the shores of Lakeport during the day have been as high as 30 ppm or more. This is a situation of oxygen supersaturation, Water Resources said.

At night, when the bacteria begin to respire or use oxygen, the dissolved oxygen concentrations plummet, bottoming out at 1 ppm or less. In the same area off Lakeport, the dissolved oxygen concentration dropped to near zero 17 nights between July 5 and Aug. 1, officials said.

Water Resources officials said these factors have come together in a perfect storm of sorts on Clear Lake – very warm water, dense cyanobacteria blooms, plenty of nutrients for the bacteria in the form of phosphorus from the landscape, wildly vacillating dissolved oxygen concentrations and fish that are already under stress in the warm water.

Officials said that, unfortunately, at this point there is little that can be done quickly to address the cyanobacteria, the phosphorus or the warm water; nature must be allowed to take its course.

Cyanobacteria blooms may at times produce toxins that can adversely affect pets and people. For this reason caution should be exercised when considering contact with the water, Water Resources said.

Avoid heavy algal scums in the water. Pets should not be allowed to swim in the lake as they may ingest the algae or scum. Caution should be exercised when young children interact with the water because they too may ingest the water and be more prone to adverse health effects due to their smaller body size, according to county officials.

Rinse off pets and people thoroughly with clean water after swimming and do not use raw lake water for cooking – boiling does not remove the toxins, Water Resources said. Before eating fish from the lake, throw away the guts and thoroughly rinse the filets with tap or bottled water.

In the long term, officials said everyone can be more careful about fertilizer use, sediment runoff and off-highway vehicle use, and the county and cities will work to better control sediment and its associated nutrient inputs off the landscape.

By working together, Water Resources officials said community members can have a significant impact on improving the water quality of the lake, the reduction of cyanobacteria blooms and the improvement of the health of fish.