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Lake Berryessa Mussel Prevention Program

During these unprecedented times, we are deeply saddened by the devastation and wish to express our solidarity with the Lake Berryessa Community.

Until further notice, the Mussel Prevention Program is on standby. 


Last Updated 08/21/2020

Lake Berryessa Invasive Mussel Inspection Protocol – PDF

Location: 1605 Steele Canyon Road, 6 miles north off highway 128

Hour of Operation:(April–September) Thurs – Mon 8:00AM-4:00PM (appointment preferred)

Contact: Zach Hyer, Water Resources Technician: 707-898-0064,

Quagga mussels were discovered in Lake Mead on January 6, 2007.Quagga 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.

Quagga mussels were discovered by Metropolitan Water District divers Wednesday, Jan. 17, 2007 at Lake Havasu, and again on Friday, Jan 19, 2007 about 14 miles to the north

Quagga Mussels (Dreissena rostriformis bugensis) are a small freshwater mollusk.  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 problem 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).

Quagga mussels can grow up to 4 cm. These mussels are indigenous to the Dneiper River drainage of the Ukraine.

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. 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 Zebra and Quagga 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

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