Holiday Weekend Boaters: Be Leery Of Invasive Mussels


The following is courtesy of the California Department of Fish and Wildlife:

Boating appears to be surging in popularity in California, and nationwide. California agencies combatting the spread of invasive quagga and zebra mussels ask new and seasoned boaters to remain cautious over the three-day Memorial Day weekend to prevent the spread of quagga and zebra mussels by cleaning, draining and drying their watercraft after each outing.

Quagga and zebra mussels are invasive freshwater mussels native to Europe and Asia. They multiply quickly, encrust watercraft and infrastructure, alter water quality and the aquatic food web, and ultimately impact native and sport fish communities. These mussels spread from one waterbody to another by attaching to watercraft, equipment and nearly anything that has been in an infested waterbody.

Invisible to the naked eye, microscopic juveniles are spread from infested waterbodies by water that is entrapped in boat engines, ballasts, bilges, live-wells and buckets. Quagga mussels have infested 34 waters in Southern California and zebra mussels have infested two waters in San Benito County, 13 of which are boatable by the public.

To prevent the spread of these mussels and other aquatic invasive species, people launching vessels at any waterbody are subject to watercraft inspections and should clean, drain and dry their motorized and non-motorized boats, including personal watercraft, and any equipment that contacts the water before and after use.

“The California Department of Food and Agriculture operates Border Protection Stations that inspect trailered watercraft entering the state” said California Department of Fish and Wildlife (CDFW) Invasive Species Program Manager Martha Volkoff. “These inspections are an integral part of preventing further introductions of mussels and are also a window into changes in boating trends. In the past two years we have seen a nearly 20 percent increase in watercraft passing through Border Protection Stations between January and May since the COVID-19 pandemic began. Because of the additional boats, we have seen more mussel-fouled boat interceptions, but more concerning, we have also seen a significant increase in the proportion of mussel-fouled boats. We attribute this to many new boaters, who aren’t aware of the mussel issue and how to prevent their spread. Memorial Day is a great opportunity to spread the word to these boaters about the simple actions they should take.”

CDFW advises boaters to take the following steps before leaving a waterbody to prevent spreading invasive mussels, improve the efficiency of your inspection experience next time you launch, and safeguard California waterways:

  • CLEAN — inspect exposed surfaces and remove all plants and organisms,
  • DRAIN — all water, including water contained in lower outboard units, live-wells and bait buckets, and
  • DRY — allow the watercraft to thoroughly dry between launches. Watercraft should be kept dry for at least five days in warm weather and up to 30 days in cool weather.

CDFW has developed a brief video demonstrating the ease of implementing the clean, drain and dry prevention method as well as a list of Watercraft inspection Programs statewide.  In addition, California State Parks Division of Boating and Waterways (DBW) has a detailed guide to cleaning vessels of invasive musselsand other information available on their webpage.

Travelers are also advised to be prepared for inspections at California Department of Food and Agriculture (CDFA) Border Protection Stations. Over the past decade more than 1.5 million watercraft entering California have been inspected at the Border Protection Stations. Inspections, which can also be conducted by CDFW and California State Parks, include a check of boats and personal watercraft, as well as trailers and all onboard items. Contaminated vessels and equipment are subject to decontamination, rejection, quarantine or impoundment.

Quagga and zebra mussels can attach to and damage virtually any submerged surface. They can:

  • Ruin a boat engine by blocking the cooling system and causing it to overheat
  • Jam a boat’s steering equipment, putting occupants and others at risk
  • Require frequent scraping and repainting of boat hulls
  • Colonize all underwater substrates such as boat ramps, docks, lines and other underwater surfaces, causing them to require constant cleaning
  • Impose large expenses to owners

A multi-agency effort that includes CDFW, DBW, CDFA and the Department of Water Resources has been leading an outreach campaign to alert the public to the quagga and zebra mussel threats.  CDFW’s invasive species e-mail,, is available for those seeking information on quagga or zebra mussels.