The Memorial Day holiday marks the kick-off of boating season in California.
As in previous years, state officials are urging boaters to be vigilant about keeping their vessels clean, drained and dried to prevent quagga and zebra mussels from hitching a ride and multiplying.
"We still need to spread the message because we need to make sure that boaters understand that it's a really serious problem."
Gloria Sandoval with the state Department of Boating and Waterways says the tiny mussels can create havoc.
"Not only for the boats but even for the pipelines that transport water, they could clog them up. So it's very costly if these quagga mussels keep spreading."
The mussels also disrupt the natural food chain and release toxins that affect other species.
Quagga mussels were found in the Colorado River 4 ½ years ago. A year later, zebra mussels were discovered in San Justo Reservoir in San Benito County.