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Public Works

County of San Luis Obispo

Invasive Mussels

Frequently Asked Questions

How are Quagga/Zebra mussels introduced into the water supply?
  • Living adult mussels adhere themselves to boat hulls, engines, and propellers and are transported from infested waters to non-infested waters;
  • Microscopic larval may survive in boat bilges, water tanks, bait tanks, fish tanks, the hull, and the trailer;
  • Aquatic plants, where adult mussels and larva live, attach themselves to boats, anchors, ropes, and trailers. The attached aquatic plants are carried to other non-infested lakes and water ways;
  • Infested fish hatcheries can transport adult mussels and larva in tanker trucks when stocking a lake with fish.
What are Quagga/Zebra Mussels?

Quagga/Zebra mussels are non-native freshwater mussels from Eastern Europe that clog waterways, undermine healthy lake ecosystems, ruin boat engine cooling systems, and financially burden water resource agencies.

Quagga/Zebra mussels are prolific breeders that can overrun a lake causing hundreds of thousands of dollars’ worth of damage annually. One female mussel can spawn 1,000,000 offspring annually. Quagga/Zebra mussels’ rapid reproduction can negatively disrupt an aquatic ecosystem in a very short amount of time. Once these mussels are introduced into a waterway, there is no way to fully eradicate the species.

What is the damage caused by Quagga/Zebra Mussels?

Quagga/Zebra mussels colonize pipes, docks, locks, ship hulls, water intake pipes, other mollusks and cause extensive damage to water treatment facilities.

Quagga/Zebra mussels disrupt the food chain by consuming nutrients used by other species. Due to massive populations, Quagga/Zebra mussels can consume so much plant life that water begins to clear up. Parks personnel in the Great Lakes region report that water once visible to depths of 6 to 12 inches have been clearing up to astonishing depths of 10 to 12 feet. Clearer water negatively affects aquatic ecosystems. Many small aquatic animals no longer have sufficient nutrients.

Quagga/Zebra mussels are filter feeders that absorb heavy metals, trace elements, toxins, and chemical contaminants in their tissues. These absorbents can be passed up the food chain when these mussels are eaten by water fowl and other organisms. There have been massive die-offs of water fowl in the Great Lakes region due to Quagga and Zebra Mussels.

Questions, comments, or concerns?

For any and all inquiries please call the County Mussel Prevention Hotline at (805) 788-6006.

Local Area Lake Mussel Prevention Programs

Public Education Materials


Documents and Information


Lake Nacimiento Mussel Inspection Program
Lake Nacimiento Resident Vessel Program