California - Aquatic nuisance species

Aquatic invasive species are non-indigenous species that threaten the diversity or abundance of native aquatic species. Two such ANS are the Zebra mussel and the Quagga mussel. States on behalf of water users spend tens of millions of dollars on attempting to control these prolific species every year.

Non-native aquatic species of plants, fish and animals are infesting the waters of California. These infestations can increase dramatically. Under the right conditions these nuisances can increase at an alarming rate and displace the native species, cause blockage of the waterways and have a negative impact on navigation and recreation.

They are next to impossible to eliminate once they are introduced. Boaters should be conscientious when pulling their boats from recreational waters. You should inspect the boat and trailer, before you leave the ramp area, and remove any suspected aquatic nuisance species and mud in order to eliminate their spread to other waters that may be visited. It is imperative to properly clean watercraft and equipment after each use. 

We recommend that you follow these steps:

  • Thoroughly check the boat and trailer for any plants or mussels.
  • Drain the water from your motor.
  • Thoroughly wash the hull of each watercraft.
  • Drain all water, and dry all areas.
  • Drain and dry the lower outboard unit.
  • Clean and dry all live-wells.
  • Be sure to report new infestations of non-native aquatic species to the U.S. Fish and Wildlife Service at (209) 946-6400.

California registered vessels using fresh water bodies within the state are required to display a “Mussel Fee Paid” sticker on the hull next to the current registration sticker. Paying the Mussel Fee does not entitle vessels to bypass inspections or fees for inspections conducted by individual reservoir owners or managers.

Visit for more information on quagga and zebra mussels or call (866) 440-9530.

California Aquatic Invasive Species

Which is an example of an aquatic invasive species?

  • Green Crab 
  • Chinese Mitten Crab 
  • Clubbed tunicate 
  • zebra mussels, 
  • quagga mussels,
  • milfoil, and
  • hydrilla

Green Crab 

Native to Europe and now established on the coast of North America as well as other non-native regions, the Green Crab is sold as fish bait in much of the world. It devours large quantities of prey, including native clams, oysters, mussels and crabs.  

Asian Kelp  

The Asian Kelp is an invasive alga that is native to Japan, northern China, and Korea. Undaria, which was first found in Southern California and has since spread to San Francisco and Half Moon Bay, most likely came to the California coast by means of hull fouling.  

Chinese Mitten Crab  

Native to the Pacific Coast of China and Korea, the Mitten Crab was first introduced to the West Coast in 1991, likely by means of ballast water or possibly by intentional releases.  

Clubbed tunicate  

The Clubbed tunicate is native to Eastern Asia and was first observed on the Pacific Coast in the 1930's. It was most likely introduced on the hulls of ships or with imported oysters (Clarke and Therriault 2007). Because of its hardy nature and ability to withstand salinity and temperature fluctuations, it has established a widespread non-native distribution.  

California Aquatic Invasive Species Management Plan

This plan proposes management actions for addressing aquatic invasive species (AIS) threats to the State of California. It focuses on the non-native algae, crabs, clams, fish, plants and other species that continue to invade California’s creeks, wetlands, rivers, bays and coastal waters.

State surveys of California's coastal waters have identified at least 312 species of aquatic invaders. These invaders cause major impacts: disrupting agriculture, shipping, water delivery, recreational and commercial fishing; undermining levees, docks and environmental restoration activities; impeding navigation and enjoyment of the state's waterways; and damaging native habitats and the species that depend on them. As the ease of transporting organisms across the Americas and around the globe has increased, so has the rate of AIS introductions.

California Aquatic Invasive Species Management Plan (PDF)