Quagga and Zebra mussels are aquatic invasive species that are not native to California lakes. They can clog drinking water intakes, and foul boat hulls, motors, and equipment left in lakes. Their sharp shells litter beaches. They harm native fish by consuming food and often kill native mussels, crayfish, and snails through fouling.

NID has assessed the vulnerability and is working to prevent the introduction of Quagga and Zebra mussels (dreissenid mussels) into three lower-elevation storage facilities: Scotts Flat, Rollins and Combie Reservoirs. Learn more here.

BOATERS ARE ASKED TO INSPECT THEIR BOATS TO PREVENT THEIR SPREAD. PLEASE MAKE SURE TO FILL OUT ONE OF THE QUAGGA SELF INSPECTION FORMS, LOCATED AT THE NID GATE HOUSES, PRIOR TO LAUNCHING YOUR BOAT AT A DISTRICT RESERVOIR.

In the late 1980s and early 1990s, these invasive mussels spread from Europe to the Great Lakes in contaminated ballast water discharged from foreign ships. From there, they expanded to the Mississippi River and later into some California waterways. They spread primarily by attaching to boat hulls, aquatic plants, docks and lifts. Adults can survive out of water for days under certain conditions.

Funding was obtained through a grant with the Department of Boating and Waterways (DBW) to develop a Vulnerability Assessment and Prevention/Monitoring Plan..

The Program assessed the vulnerability of these reservoirs to the introduction of non-native dreissenid mussel species by:

• Monitoring the number of visitors
• Inquire as to the origin of visitors (relative to Dreissenid infested waters)
• Monitor outside equipment that is allowed (rentals)
• Survey the duration of use (day use, slipped/moored)
• Monitor access (managed or unmanaged)
• Prevention efforts being implemented
• Education efforts being implemented

The ongoing program aims to prevent the introduction of non-native dreissenid mussel species and includes, at a minimum, all of the following:

•  Public education consisting of handouts, flyers, signage, postings and verbal communication
• Monitoring that consists of applying substrate for the adult and/or larval mussels and water quality conditions to determine viability of adult and/or mussels survival
• Management of recreational, boating or fishing activities that are permitted, which may include inspections, decontamination stations and/or information where to decontaminate a vessel, exit inspections and banding of vessels to trailers

Read NID's Quagga/Zebra Mussel Vulnerability Assessment Report and Prevention/Monitoring Plan 

The USGS has put together an interactive map of waterways where invasive aquatic species have been found. Quagga and zebra mussels are currently located in a number of lakes and waterways in California.