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Hydrilla Detected in Clear Lake Keys

LAKEPORT, August 7, 2019 – The Lake County Water Resources Department will be supporting the Lake County Agricultural Commissioner, and the California Department of Food and Agriculture, in an extensive survey in response to a recent detection of hydrilla within the Clear Lake Keys area of Clear Lake in Lake County.

The detection was confirmed on August 1, 2019.  The detection was made as part of the coordinated aquatic invasive species prevention program that protects aquatic resources in Lake County.  Early detection is a key component to successfully eradicating a hydrilla infestation before it becomes established.  Ongoing detection surveys are conducted throughout Clear Lake, and for more than two years, no hydrilla (Hydrilla verticillata) has been seen or detected.  

“With no detections of hydrilla for over two years, this recent detection shows that we cannot become complacent, we must be vigilant in our efforts to fully eradicate this invasive species,” said Angela De Palma-Dow with the Lake County Water Resources Department.  “The public’s help is vital to the eradication effort.  We thank the public and, specifically, the Clear Lake Keys Property Owners Association for their cooperation and continued communication throughout this project.”

Program partners will conduct an extensive survey, also known as a delimitation survey that includes the keys and some of the area immediately surrounding the detection site.  Officials use special hooks, placed in the water, to capture pieces of hydrilla.  If a piece of hydrilla is hooked, officials immediately stop the hooking operation and take GPS coordinates.  Officials then visually look for any floating hydrilla remnants to ensure that viable plant pieces do not float off to other parts of the lake and start a new infestation.

Following the principles of Integrated Pest Management, officials use chelated copper in order to eliminate any viable, living hydrilla fragments, stems and leaves, preventing an infestation.  In addition, an organic formulation of Sonar SRP (slow release pellets), also known as Fluridone, is used.  The pellets sink to the bottom of the lake in the immediate and surrounding area around the detection site and serve as a pre-emergent, preventing the sprouting of any remaining hydrilla tubers and turions.  The pellets have low toxicity to animals, including fish, and there are no restrictions on swimming or drinking in treated water bodies.  All treatments comply with the National Clean Water Act – National Pollutant Discharge Elimination System.  The Hydrilla Eradication Program has a positive and proven track record of eradication in California, having eradicated hydrilla from 15 counties since 1976.

In addition to the treatments, the Lake County Water Resources Department has issued stop-order notices to mechanical harvesting permit holders and others in the immediate detection area of Clear Lake Keys.  The Water Resources Department is also urging the public to reduce any unnecessary boat traffic from the Keys into the main body of Clear Lake until surveys and treatments are completed.

Reducing mechanical harvesting and limiting boating traffic can significantly limit the probability of transporting hydrilla plants and plant fragments from the Clear Lake Keys to other locations in Clear Lake, or to another body of water.  Hydrilla, much like other aquatic plant invasive species, can rapidly reproduce from a small stem fragment, which can float through lake currents or be picked up by a boat and travel to other parts of the lake, where it can start a new infestation.  Hydrilla fragments can grow over an inch in length per day and can double their mass every two weeks under ideal conditions.  

The Lake County Water Resources Department reminds the public that removal or control of any aquatic plants in Clear Lake, whether by hand-pulling, mechanical harvesting, or chemical treatment, requires a permit.  The Clear Lake Aquatic Plant Management Permit application can be found here, “Aquatic Plant Management,”  or on the Aquatic Plant Management tab on the County of Lake Water Resources Department Website.  The application can be printed and filled out in hard copy or downloaded electronically and emailed to the department.
Hydrilla is a non-native, aggressive, submerged aquatic invasive plant species which can cause severe damage to both our natural environment and economy of Clear Lake.  Once hydrilla invades an aquatic ecosystem, it drives out all native aquatic plants, creating a pure stand of hydrilla, further outcompeting other plant species for space and light (Bates and Smith 1994).   

Hydrilla breaks apart very easily and small pieces of stem, no more than one inch long, can produce entire new plants. The plant produces special survival structures on the stems, called turions, and in the sediment, called tubers. Each tuber also produces a new plant. The tubers can survive for 7 to 9 years in the sediment before sprouting, even if no water is present for much of that time.  The presence of hydrilla populations can also have negative impacts on aquatic wildlife.  Sportfish surveyed from other lakes where hydrilla is the dominant aquatic plant species have been shown to be smaller in weight and size, as hydrilla limits spawning and foraging space available to fish, and creates an unsuitable environment for the primary fish food source, zooplankton and phytoplankton (Colle and Shireman 1980).

Hydrilla also interferes with boating and fishing, and increases the risk of drowning by making it difficult to swim in safety (Langeland 1996).  Heavy hydrilla infestations decrease fishing stocks, and, along with the impact on boating, reduce recreational opportunities, and the local economies these activities support.
There are several native aquatic plants in Clear Lake that look like hydrilla, such as coontail and elodea. Hydrilla outreach materials have been posted in green educational kiosks located at several of the boat ramps around the Clear Lake keys. Residents who believe they have seen hydrilla are encouraged to contact Lake County Water Resources Department’s Aquatic Invasive Species Program Coordinator, Angela De Palma-Dow at 707-263-2344, by visiting our website at, or message us directly on Facebook Lake County Water Resources Department, @lakecountywater.

All sources cited in this press release can be found at the USGS Nonindigenous Aquatic Species Database for Hydrilla available at: Revision Date: 4/25/2018, Access Date: 8/6/2019

HydrillaIMAGE 1.

Hydrilla can be recognized by the whorled pattern of five leaves around a central stem and distinguishable teeth, or serrations, along the leaf edges and also on the central midvein. Elodea has leaves in whorls of three, and no teeth along the leaf edges or midvein. Egeria has leaves in whorls of four or eight, with slightly serrated leaf edges but no teeth on the midvein.

HydrillaIMAGE 2.

If you think you see hydrilla, grab a section and take a photo in your hand, as shown in the image. Send it to [email protected] . Take note of the location (lat/long coordinates) and DO NOT THROW the fragment back into the lake.  Place fragment in a plastic zip-top bag for further identification by County and CDFA. (Image curtesy of LSU Ag Center)


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Urgent Health Advisory

Effective immediately, people on private water systems whose tap water comes from their own private intake into the lake, in the Oaks Arm and Lower Arm of Clear Lake should not drink the water.

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