For more than 50 years, Nacimiento and San Antonio reservoirs have provided agricultural, residential and industrial water supply as well as recreational benefits. The lakes attract thousands of boaters, swimmers and fishermen every year. It has been a valuable investment that needs to be protected.

That's why we're asking you, before you visit Nacimiento and San Antonio reservoirs, to take a few moments to learn about how you can prevent an invasion of Quagga and Zebra mussels to these valuable resources. If we're all vigilant, we can stop these invasive aquatic species from spreading to our reservoirs.

          Boaters are required to have an inspection and carry the vessel screening permit on the boat
          Vessel Screening Form
          2012 Quagga and Zebra Mussel Prevention Program at Lake San Antonio and Lake Nacimiento


Quagga and Zebra mussels are aquatic invasive species that are not native to Nacimiento and San Antonio Reservoirs. If these mussels get into the lakes, they are likely to cause economic and/or environmental harm. The impact of these mussels cannot be overstated. They will displace native species, disrupt ecosystems and harm recreational activities such as boating and fishing. They are likely to also cause considerable financial losses for water supply and commercial activities around the lakes. They have the potential to foul the workings of the dams and the new San Luis Obispo County water delivery system, and to reduce property values around the reservoirs.


Quagga and Zebra mussels grow in dense clusters, like barnacles. The microscopic larvae reproduce quickly and thrive in California's warm Mediterranean climate. Quagga mussels were found in Southern California waters in 2007. These mussels pose imminent risks to California's waterways. The costs of managing these mussels in California could reach hundreds of millions of dollars.

 WHERE ARE THEY NOW? (Mouse-over map)

In January 2008, Zebra mussels were found as close as San Justo Reservoir in Hollister. Worried that the recreational boaters of San Justo would introduce the mussel to other reservoirs in the state, San Benito County Public Works officials have closed San Justo Reservoir to all boating activity.

 SOLUTION (Don't move mussels from one place to another)

Currently, Zebra mussels are not known to occur in any other California water bodies, but efforts to educate the public and prevent more widespread introduction is underway. It is up to you as an individual boat or pet owner or fisherman to take preventative measures to ensure that the mussels don't travel wih you.


The mussels can be transported by recreational boaters and fishermen via boat hulls, motors, ballast water, live bait and other gear, including clothing. What you can do is thoroughly inspect and dry all of your equipment that contacts the water and don't bring in live bait from outside sources. Also, if your pets enter the water, they should be inspected and dried, too. And please use your imagination when cleaning your boat, gear and clothing. Where would you hide if you were a mussel?

Where to Inspect Your Own Boat
TAKE NOTE! Boaters are required to have an inspection and carry the vessel screening permit on the boat


For more information about inspection, the history of aquatic invasive species migration and how you can become involved in stopping the hitchhikers, here are some links:

  1. San Luis Obispo County Public Works
  2. Santa Clara County Parks
  3. Santa Clara Valley Water District
  4. San Benito County Parks
  5. Santa Barbara County Parks

  6. Pinto Lake
  7. California Department of Fish and Game
  8. 100th Meridian Initiative
  9. California Department of Boating and Waterways
10. U.S. Fish and Wildlife Service

Vessel Screening Form

 2013 Quagga and Zebra Mussel Prevention Program at Lake San Antonio and Lake Nacimiento


Mussel Hotline 1-866-440-9530