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Lake Berryessa Mussel Prevention Program

by cooperating with our inspection and decontamination process

Funding of this Program is provided in part by the Division of Boating and Waterways

The contents of this page do not necessarily reflect the views and policies of Division of Boating and Waterways, nor does mention of trade names or commercial products constitute endorsement or recommendation of their use. 


If you have questions about the program or need to schedule a watercraft decontamination, please contact Drew Gantner at 707-914-5356 or

Decontamination Location

Steele Canyon Recreation Area, 1605 Steele Canyon Road, 6 miles north off highway 128

Hours of Operation

April–September, Thurs – Sun, 8:00AM-4:00PM (appointment preferred)

Frequently Asked Questions

Does Lake Berryessa have mussels?
Lake Berryessa is mussel free! The Asian Clam, which can be found in Lake Berryessa, is
commonly mistaken as a zebra or quagga mussel but they do not pose the same threat.

How do you know Lake Berryessa does not have zebra or quagga mussels?
Solano County Water Agency regularly samples the waters of Lake Berryessa and the Solano Project for the presence of larval and adult quagga or zebra mussels as part of our early detection monitoring program. There are biologists on staff who are trained in the microscopic evaluation of plankton samples for the detection of larval mussels in our water supply. CDFW and USBR also conduct tests to ensure Lake Berryessa is negative for zebra or quagga mussels.

Why do I have to go through this inspection process?
The best way to keep Lake Berryessa mussel free is to ensure each boat entering the water does not pose a risk of harboring mussels. This is done through the screening questions conducted by Lake Berryessa staff including SCWA Watercraft Inspectors, USBR Rangers, and Concessionaire employees. The green watercraft seals are intended to identify boats who last launched at Lake Berryessa that we know are mussel free, eliminating the need for further

Should I get my boat decontaminated?
Below are indicators you should call to schedule a decontamination:

• You purchased a boat in the past month and cannot verify where it last launched.
• You purchased a boat that came with standing water you cannot verify where from.
• You launched you boat in the past 30 days or STILL have standing water from a waterbody in Southern California or out of state

What to do if you think you have been to an infested waterbody

Quagga and Zebra Mussel Facts

Quagga Mussels (Dreissena rostriformis bugensis) are a small freshwater mollusk.  They are an invasive species native to Russia and Ukraine and are thought to have been transported to the Great Lakes region in the ballast water of transoceanic ships. They have some diagnostic features to identify them from zebra mussels.  The quagga’s shell has a rounded angle, a convex ventral, and their color varies from black, white, cream, but they are generally paler (U.S.G.S.). The quagga causes problems because they are “water filterers” and are able to remove large amounts of phytoplankton and suspended particulates from lakes and streams (Sea Grant Michigan). This can have a potential to alter the balance of the aquatic food web.  The mussels’ tissues also trap contaminants, which can be exposed to wildlife if they are eaten.  Like zebra mussels, the quagga also clogs water structures that can reduce pumping capabilities for water treatment (Sea Grant Michigan).

Zebra mussels, a native species of Eastern Europe, were first introduced in the United States through ballast water released into the Great Lakes in the late-1980s. Quagga mussels soon followed.

Great efforts have been made to prevent the spread of these fresh water mollusks west of the 100th Meridian. In January 2007, Quagga mussels were discovered in Lake Mead and later in other reservoirs of the Lower Colorado River. Quagga mussels were discovered by Metropolitan Water District divers on Wednesday, Jan. 17, 2007 at Lake Havasu, and again on Friday, Jan 19, 2007 about 14 miles to the north. In January 2008, Zebra mussels were discovered in San Justo Reservoir in San Benito County, California. The spread of these mussels to additional California waters will seriously impact the state’s aquatic environment and water delivery systems, endangering recreational boating and fishing.

What Makes These Mussels So Invasive?

As adult mussels, there are three characteristics that make them incredibly invasive:

  • BYSSAL THREADS – Both zebra and quagga mussels have byssal threads that allow them to attach to any stable substrate in the water including rocks, plants, fiberglass, plastic, cement, steel, and even onto other mussels creating a thick layer as seen in some of these photos.
  • RAPID REPRODUCTION RATE – They have a very rapid reproduction rate, spawning year-round (if conditions permit), where 1 single female can produce up to one million eggs in a year.
  • FILTER FEEDERS – Feeding off of plankton (the foundation of the aquatic food chain). It has been observed that a mussel can filter up to a liter in a day. Anything they have filtered through that they do not eat is rejected as a mucous known as pseudofeces. This pseudofeces is known to decrease DO and increase pH.

Last Updated 1/9/2024

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