Hundreds of dead fish washed up on the shores of Clear Lake earlier this week, most likely suffocated by a shortage of oxygen in the water.
Such events are not unusual for Clear Lake, said Phil Moy, director of Lake County Water Resources.
“The water was literally like pea soup” in the areas where the fish died, he said, estimating one dead fish per foot of shoreline.
Oxygen depletions are a common cause of fish kills. Algae is usually a major source of oxygen and during daylight hours normally produces oxygen as a by-product of photosynthesis. But some situations can reduce the amount of oxygen algae produces, such as trace minerals and nutrients needed by the algae being used up. When the algae dies, the bacterial decomposition and loss of oxygen production can lead to oxygen depletion and fish kills. Fish become stressed and can die when oxygen levels drop below 4 or 5 parts per million, Moy said.
Clear Lake oxygen readings for this week were not available Thursday.
The dead fish were concentrated in sheltered areas near Clearlake Oaks and the narrows near Buckingham, but also were reported in several other locations.
Angelea Turner, 25, who works at Oak’s Red and White Store in Clearlake Oaks, said the die-off “looks pretty sad. I’ve never seen it like this before.”
Terry Knight, who’s been observing and writing about Clear Lake and fishing for three decades, said most of the dead fish were threadfin shad but there also were larger fish, including catfish and bass. Normally, the larger fish swim to deep water to breathe, but young fish prefer to stay closer to shore, where they’re more likely to die.
The situation was improving by the end of the week, thanks to increased winds stirring up the water and increasing oxygen levels, he said.
At Lakeport’s Library Park, fish were aided by algae-clearing aerators. Knight said in Glenhaven, east of Clearlake Oaks, the owner of Indian Beach Resort came to the aid of the fish by starting up the engines of boats docked at his pier. Many of the gasping fish there immediately recovered, he said.
The die-off is unlikely to impact fishing on Clear Lake, which is enjoying a boom in bass populations, he said.