The recent record-setting hot temperatures apparently have had an impact on the fish in Clear Lake. Hundreds of carp, catfish, crappie and bass have died in the Lakeport area, the most recent deaths occurring over the weekend.
On Sunday morning, I launched my boat at the Fifth Street Ramp in Lakeport and headed north. As I was passing Rumsey Bay, I saw hundreds of dead carp floating in the water. There were approximately 700 dead carp and a lesser number of bass and catfish. A check of the carcasses showed they had probably died sometime Saturday night as all the fish were still fresh.
On Monday, I accompanied Department of Fish and Game (DFG) Senior Biologist Rick Macedo on a boat tour from Library Park in Lakeport to Rocky Point. We were looking for dead fish and found hundreds scattered all along the shoreline.
What was unusual was that in the area from Rumsey Bay to about a half-mile up the shoreline nearly all the dead fish were carp. However, from that point to Rocky Point, there were few dead carp but hundreds of dead bass, crappie and catfish.
Why the fish died so suddenly is unknown. There are several theories that range from weed eradication to the recent hot weather or even a combination of the two. I did receive two telephone calls from individuals who said they observed an air boat spraying the weeds north of Lakeport last week. Only a state-licensed weed eradication contractor can be used and a permit for each spraying is required by the county.
When weeds die they use up oxygen as they decompose. This could have caused the massive die-off or it could have been the hot weather alone. According to Macedo, when the dissolved oxygen (DO) levels drop suddenly, fish often die in less than an hour.
Dissolved oxygen consists of gas molecules that form in the water. Fish use DO the same as humans do when they breath oxygen into their lungs. The exception is that fish have gills instead of lungs and they extract the oxygen molecules from the water as the water passes through their gills. DO gets into the water by aeration such as waves, running water and surface disturbance. Living aquatic plants also create oxygen.
When the water temperatures reaches 90 degrees or more, the DO is used up rapidly and there is less oxygen for the fish. DO is measured in parts per million and the scale ranges from zero to 10 10 meaning a rich supply of oxygen and zero meaning no oxygen.
Macedo said that bass can tolerate DO levels of four, but when it drops below four the fish become stressed. Catfish and carp can tolerate DO levels as low as two.
DO reaches it lowest level during the night and Macedo said that”s when most of the fish probably died. During the daylight hours aquatic plants create oxygen in the water through photosynthesis, the same as trees and ground plants do. However, these same aquatic plants use up oxygen at night, which can deplete the DO from the water. Also, when plants die they use up DO as they decompose. Macedo said that most of the fish probably died in the shallow bays, where the DO is the lowest. The bays are protected from the winds and the water temperatures are normally much higher there.
Most of the fish die-off occurred in the north end of the lake in the north Lakeport area. There also have been reports of dead fish in Cache Creek and the Clearlake Oaks Keys.
Even though several thousand fish died in the recent die-off, it pales in comparison to 1987 when tens of thousands of carp and other fish died in Clear Lake. In fact, dead fish were packed on the beaches from Nice to Clearlake Oaks and it took nearly a week to pick up and dispose of the carcasses.
Bass fishermen are wondering if the latest die-off will hurt the outstanding bass fishing on the lake. The answer as it now stands is probably no. However, if the die-off continues, it could have an impact. Many of the dead bass found on Monday weighed between 4-6 pounds.
Macedo said he doubts the fish die-off was due to a virus or pollution in the lake.
“This occurs all the time in many lakes and it”s almost always due to oxygen depletion,” Macedo said.
The big problem for the City of Lakeport and county is cleaning up the dead fish. The fish are scattered along the shoreline for several miles and it will take a concentrated effort to remove them.
The other problem is that with hot weather forecast for the next few days, the stench of the dead fish won”t make sitting on the decks of the lakeside homes a pleasurable event.
