Clear Lake is one of the richest lakes in the state when it comes to nutrients. That is one reason we have algae blooms as well as a massive amount of aquatic weeds. Some of the species of aquatic weeds have been in the lake for more than a million years and others only a few years. These new arrivals are classed as foreign invasive weeds. For example, the well known weed, hydrilla, is classed as an invasive weed and originally came from India. It was actually imported as an aquarium plant back in the early 1950s. In fact, at one time you could buy hydrilla plants from garden shops in Lake County. It is believed to got into Clear Lake by someone emptying an aquarium containing hydrilla off their dock into the lake. There is so much concern about hydrilla that the State of California keeps an eradication crew assigned to the lake full time.
The lake is home to an estimated 35 different species of weeds and two-thirds of them are non-native or what are called “invasive weeds. In the past the county hired firms to cut the weeds but two years ago the county decided to spray the weeds with a herbicide. Herbicide companies will spray a 100 foot swath along designated shorelines and at entrances to public boat ramps. The lakeside residents will be responsible to hire a contractor to spray the areas around their docks. There has been a concern that using a herbicide spray will harm the fish. Unlike mechanically cutting the weeds which will regrow after a short time, spraying the weeds with a herbicide kills the weeds down to the roots. The problem can be as these weeds die they will use up the oxygen in the water which will can impact the fish. But in most cases the fish will just leave the area.
Other weeds that are of concern are the sago pondweed, a plant native to Clear Lake. This is the long stringy weed that breaks loose and forms mats. Later in the summer other species of weeds such as primrose and duckweed will be sprouting. There is also an invasive plant called Eursian Watermillfoil that is spreading rapidly around the lake.
According the Lake County Water Resource Department, During 2018-2019 the nuisance aquatic plants most commonly found and controlled in Clear Lake include but are not limited to: native sago pondweed, , invasive curlyleaf pondweed and invasive creeping water primrose.
With the approval of the CA Department of Fish and Wildlife, aquatic herbicides will be applied to Clear Lake in June and continue (with approval) periodically through October. Water use restrictions or precautions are the responsibility of the licensed aquatic herbicide applicators. To get a permit to remove the weeds and for more information contact Angela Palma-Dow, Invasive Species Program Coordinator at (707) 263-2341.
The weed mats that form from dying weeds have little impact on the fishermen. As long as they don’t allow the weeds to clog up the water intakes on the outboard motors they can handle them just fine. In fact, many of the bass fishermen prefer heavy weed growth because they claim it improves fishing. However, it’s just the opposite for the wakeboard boats and pleasure boaters. They hate the weeds because it makes boating just about impossible in many areas.
Sago pondweed is considered a pest in some parts of the world. It can become quite thick in shallow waterways such as Clear Lake and since it spreads via rhizomes and seeds, it has a high capacity to reproduce. It is a valuable food plant for wildlife, particularly waterfowl. Diving ducks rely on the tubers as a food source and many dabbling ducks will eat the foliage and seeds. Sago pondweed, as part of a diverse aquatic plant community, also provides valuable habitat for small invertebrates and young fish that forage among its branches and use its dense growth to hide from predators. Excessive weed growth can have an impact on the adult fish such as bass. The thicker the weeds the more difficult it is for the bass to locate their prey.
Weeds and algae are just part of living on Clear Lake and it doesn’t appear it will change anytime soon.
