Few things have sparked as much interest or created as much controversy as the fish die-off that occurred in late July. The fishing websites have been alive with accusations that the fish kill was caused by either California officials or private companies because of the spraying of herbicides on the lake to kill aquatic weeds.
It’s the state’s spraying to kill hydrilla that has drawn much of the heat from anglers. According to a spokesman for the California Department of Food and Agriculture (CDFA), the state only sprays to control hydrilla, not other aquatic plants. Lake County Water Resources Department is responsible for controlling the other aquatic weeds in the lake.
CDFA does have an aggressive program to control hydrilla, which was first discovered in Clear Lake in 1994. It is believed that it got into the lake after someone dumped the contents of an aquarium into the lake water. At one time hydrilla could be purchased at your local nursery.
It is an aggressive aquatic plant, one that infests natural and manmade aquatic ecosystems. CDFA conducts eradication efforts in nine counties throughout California using various methods of control. The largest eradication effort is at Clear Lake.
According got CDFA, surveying for hydrilla in Clear Lake is a challenge. Until 2011, surveys covered from the shoreline out to between 600 to 800 feet from shore, so the area to be surveyed in one circuit of the lake’s 100-plus miles of shoreline was about 7,300 acres (about 11 square miles). In addition, hydrilla is actually scarce in Clear Lake now. It takes a great deal of work to find the plants. For instance, the crews found 76 plants in 2009 but that represents a tiny area in a 43,000-acre lake.
Square miles of Clear Lake’s area are also heavily covered in submerged weeds, which interfere with surveys. To date this year, crews have found only two plants, one n Corinthian Bay and the other in the south end of the lake. When a crew finds a plant, a 5-acre area around the plant is marked off and a copper-based herbicide is applied to kill the exposed parts of the plant. However, in most cases the roots are still alive. A few weeks later the area around the plant is sprayed with a pellet-style herbicide called “SONAR.” The Sonar penetrates down to the roots of the hydrilla and kills the plant.
Hydrilla roots can remain dormant for years and before they resprout. Before applying any herbicide, the CDFA crews take a water temperature and dissolved oxygen (DO) reading. If the water is too warm and the DO too low, spraying is delayed. The fish die-off took place July 27 in Rumsey Bay, located in Lakeport. The CDFA last sprayed on June 2 and the spraying that took place was nowhere near Rumsey Bay. Experts say the cause of the fish kill was probably related to high water temperatures and a drop in the DO. At the time of the fish kill water temperatures were as high as 90 degrees in some areas.
Contrary to what many bass fishermen believe, hydrilla is bad for the bass fishery. If allowed to spread unchecked the entire lake would be choked with the weed and boating and fishing would be impossible. This has already happened in several Florida lakes.
The CDFA has six airboats stationed at Clear Lake. The reason airboats are used is because if boats with outboards traveled through a hydrilla patch there is a good chance the props will cut up the hydrilla, allowing pieces of the plant to drift to a new area and take root again. The crews on the boats spend most of their time dragging large hooks along the lake bottom looking for hydrilla plants. To date, the 12-year project to control hydrilla on Clear Lake has been extremely successful. Clear Lake is the largest lake in the country where hydrilla has been successfully controlled.
