Clear Lake is always full of mysteries. Recently there have been reports of a large mass of dead fish being seen along the shoreline at Nice and Lucerne. The cause of the die-off has blamed on a low dissolved oxygen caused by blue-green algae. The fish species consisted of bass, carp, crappie and catfish.
Normally when a first dies it floats for a short time because of the air in its air bladder. The air bladder’s purpose it to allow the fish to swim upright and have some buoyancy. The fish fills his bladder by ingesting dissolved oxygen (DO). When it dives it expels the oxygen to reduce buoyancy. After the fish dies there is no more DO being ingested and the air in the bladder starts to dissipate and the fish sinks to the bottom. After a few days, the internal organs of the dead fish decompose and a gas is formed. This gas causes the fish to once again float. Once the gas is dispersed the carcass will once again sink to the bottom, where it will gradually break apart. At any given time in a lake such as Clear Lake there are thousands of fish carcasses decomposing on the bottom of the lake. I have seen this with my underwater camera. A similar situation occurs when a human or other mammal drowns. Initially, the human will sink to the bottom and often the body will stay there for several days. As gasses form in the body due to tissue breakdown the body will rise to the surface.
I took DO readings on Sunday along parts of the Nice to Clearlake Oaks shoreline and they ranged from as high as 3 to as low as 1. Bass, crappie and bluegill require a DO of at least 3 to survive for any length of time. When the DO drops below 2 they are in deep trouble. A similar analogy would be if you hiked to the summit of a 18,000-foot mountain. You would find breathing to be extremely difficult.
The other factor that is occurring is that in the areas where the fish were dying, the success rate for fishermen has dropped to nearly zero.
Several things could explain why the fishing has dropped off completely. The dead fish that sunk to the bottom decomposed and that action used up the DO in the water. The results are that the live fish moved out of the area to a more oxygen rich area. The other reason could just be a lack of live fish due to the massive die-off which depleted the population.
The good news is that as we move into the late summer and fall months the temperatures will drop at night and the DO will go up and the die-offs will subside.
Even with the tens of thousands of fish that have died, the overall population of all species of fish in the lake is in good shape. Clear Lake has more fish per acre than any other lake in country.
Fishery biologists have told me that when the fish population in a lake exceeds the food and habitat available there will be die-offs. The same goes for all wildlife. It’s nature’s way of ensuring that the fish will survive. Given time, Clear Lake will recover and the fishing will be as good as ever.
