Aquatic Invasives

Take Action Against Aquatic Invasives

  • Help the Invasive Species Program launch a statewide citizen science effort to monitor for quagga mussels.
  • Find out which species are threats to California. Learn alternatives to releasing unwanted fish, aquatic plants, and other pets.
  • Eat them. Yes, really. Check out this interesting website to find out who is edible and how to prepare them
  • Share your knowledge.
  • Have you spotted an invasive species? Report your sighting.
  • If you own a boat, you can prevent the spread of aquatic invasive species using this checklist every time your exit a waterbody:
  • Inspect all watercraft and equipment.
  • Clean any visible mud, plants, fish or animals from watercraft and equipment.
  • Drain all water, including from lower outboard unit, ballast, live-well, buckets, etc.
  • Dry all areas.
  • Dispose of debris and live bait in trash.

The Problem of Aquatic Invasives

What are Aquatic Invasives?

Invasive species are organisms (plants, animals, or microbes) that are not native to an environment, and once introduced, they establish, quickly reproduce and spread, and cause harm to the environment, economy, and/or human health.  Relatively few non-native species had been introduced to California prior to its settlement by Spaniards, which began in the 1700’s. With the beginning of European settlement, non-native species were carried to California attached to the hulls of ships, submerged in the ships’ ballast, or carried along in shipments of grain. Californians have benefited from the introduction of many plant and animal species necessary for food or other human pursuits; however, a small proportion of introduced species have become invasive and are wreaking havoc on the state’s environment and economy.
Today, there are many different ways in which non-native invasive species are introduced to California. Commercial shipping remains a major source of unintentional introductions, along with smaller commercial fishing boats and recreational watercraft. People traveling between natural areas, farms, or waterways for work or recreation unintentionally spread invasive species on their vehicles, boats, equipment and even clothing.

Shipping is also a major mechanism by which aquatic invasives are transported around the globe. Shipping is responsible for or has contributed to 79.5% of established aquatic NIS introductions in North America (Fofonoff et al. 2003). Commercial ships transport organisms through ballast water and vessel biofouling. Ships use ballast water to maintain stability at sea, and when ballast water is loaded in one port and discharged in another, the entrained organisms are introduced to new regions.

Both historically and today, non-native invasive species have also been introduced purposely, without an understanding of the potential consequences of those introductions. This occurs most commonly with plants used for erosion control, livestock forage, and aquarium or garden ornamentals. Some of the animals that are currently, or were in the past, brought into California as sources of food, fur, or pets have turned into major pests.

Why are they a problem?

Invasive species threaten the diversity or abundance of native species through competition for resources, predation, parasitism, interbreeding with native populations, transmitting diseases, or causing physical or chemical changes to the invaded habitat. Through their impacts on natural ecosystems, agricultural and other developed lands, water delivery and flood protection systems, invasive species may also negatively affect human health and/or the economy. Examples of direct impacts to human activities include clogging navigable waterways and water delivery systems, weakening flood control structures, damaging crops, introducing diseases to animals that are raised or harvested commercially, and diminishing sportfish populations.

A large population of an invasive species can start from a very small number of individuals, and those individuals can be difficult to see, so they may easily go unnoticed. The tiny young of invasive shellfish or insects, a fragment of an aquatic weed, or a single plant ready to release its seeds can be enough to establish a population that could ultimately cost the state millions of dollars to address. The longer infestations are allowed to progress, the more extensive the damage and control costs, and less efficient the control efforts. However, if populations are detected early enough, eradication may still be possible. Though prevention is the best strategy for managing invasive species, “early detection and rapid response” efforts are the most effective and cost-efficient responses to invasive species that become introduced and established.

State surveys of California’s coastal waters have identified at least 312 species of aquatic invaders. As the ease of transporting organisms across the Americas and around the globe has increased, so has the rate of aquatic invasive introductions. For example, the invasive overbite clam was introduced from Asia to California and has been linked to the decline of endangered delta smelt. The delta smelt is recognized as an important indicator of ecosystem health, and is also threatened by water pollution. Researchers believe that the overbite clam removes key microorganisms from the water, which form the basis of marine food chains. Without these microorganisms, smelt and other fish species starve.

Commonly Found Aquatic Invasives

Quagga and Zebra Mussels (Dreissena bugensis and Dreissena polymorpha)

Clogging of pipe by mussels Image: Mussel Prevention Program, San Luis Obispo, CA

Clogging of pipe by mussels Image: Mussel Prevention Program, San Luis Obispo, CA

Quagga and Zebra mussels pose a serious threat to our waters and fisheries. The spread of these mussels threatens recreational boating and fishing, aquatic ecosystems and fisheries, water delivery systems, hydroelectric facilities, agriculture and the environment in general. Both quagga and zebra mussels are native to Ukraine and Russia and may have been introduced to the United States from ballast water of trans-oceanic ships. To date, quagga mussels have been found in water bodies in San Diego, San Bernardino, Orange, Riverside, and Imperial counties.  These mussels wreck havoc on the environment, disrupting the natural food chain, can contribute to the release of harmful bacteria that affect other aquatics, and can clog pipes that may be used to transport or discharge water.


Water Hyacinth (Eichhornia crassipes)

Water hyacinth clogs waterways Image: Bob Case

Water hyacinth clogs waterways
Image: Bob Case

Water Hyacinth is an attractive floating aquatic plant with shiny green leaves and delicate lavender flowers and was introduced into the Delta from South America more than 100 years ago. This extremely prolific aquatic invasive plant can double in size every ten days in hot weather and can quickly become a dense floating mat of vegetation up to six feet thick. The mats can travel with river currents and with tidal movement and can also attach to structures in the water, limiting access to boats and reducing swimming areas.




Brazilian Elodea (Egeria densa)

Brazilian Elodea can displace native plants and block light needed for photosynthesis Image: Alan Cressler

Brazilian Elodea can displace native plants and block light needed for photosynthesis
Image: Alan Cressler

Brazilian Elodea is a shallow-water submerged aquatic plant from Brazil, popularly used as an aquarium accessory that was introduced into the Sacramento-San Joaquin Delta about 40 years ago (possibly from use in home aquariums). Similar to the water hyacinth, this submerged vegetation now infests many thousands of surface acres of the Sacramento-San Joaquin Delta. The plant can spread very quickly depending on environmental conditions, often by fragmentation. It displaces native plants, blocks light needed for photosynthesis, reduces the amount of dissolved oxygen in the water and deposits silt and organic matter several times the normal rate.

What is the State of California Doing?

In California, many state agencies have authority over and regulatory roles for managing natural resources. While diverse agencies have some authority to regulate aquatic invasive species, there has been no centralized authority or management structure to coordinate AIS activities before the development and implementation of California’s Aquatic Invasives Species Management Plan. This plan proposes management actions for addressing aquatic invasive species threats to the state and 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.

Through the Management and Control Act, the CA State Lands Commission, the California Department of Fish and Wildlife, and the State Water Resources Control Board and the Board of Equalization work together to research, develop policy and management plans, and monitor aquatic invasives.  This law also requires vessels arriving to California from outside the U.S. Exclusive Economic Zone (EEZ; 3 to 200 miles outside of state waters) to manage their ballast water before discharging into State waters. Additionally, each vessel that arrives at a California port or place must comply with reporting and inspection requirements.  In 2003, it was revised and reauthorized with new recommendations.

The California Department of Fish and Wildlife (CDFW) operates an invasive species program with a mission to reduce the negative effects of non-native invasive species on the wildlands and waterways of California. CDFW are involved in efforts to prevent the introduction of these species into the state, detect and respond to introductions when they occur, and prevent the spread of invasive species that have become established. CDFW conducts work in coordination with other government agencies and non-governmental organizations and tries to identify and address the ways by which the species are introduced, typically inadvertently, by human activities.  The Marine Invasive Species Program also exists within the Department of Fish and Wildlife, Office of Spill Prevention and Response and coordinates with the California State Lands Commission to control the introduction of aquatic invasives from the ballast of ocean-going vessels.

What is the Federal Government Doing?

California’s aquatic invasives species management efforts must also be coordinated with the federal government’s extensive efforts on the same front. No single federal agency has comprehensive authority for all aspects of aquatic invasive species management. Federal agencies with regulatory authority over the introduction and transport of aquatic invasive species include the U.S. Department of Agriculture Animal Plant Health Inspection Service, the U.S. Department of Agriculture Agricultural Marketing Service, the U.S. Fish and Wildlife Service (USFWS), the U.S. Department of Commerce (DOC), and the U.S. Coast Guard (USCG). Many other agencies have programs and responsibilities that address components of aquatic invasives species, such as importation, interstate transport, exclusion, control and eradication.

The Aquatic Nuisance Species (ANS) Task Force is an intergovernmental organization dedicated to preventing and controlling aquatic nuisance species, and implementing the Nonindigenous Aquatic Nuisance Prevention and Control Act (NANPCA) of 1990. The ANS Task Force consists of 13 Federal agency representatives and 12 Ex-officio members, and is co-chaired by the U.S. Fish and Wildlife Service and National Oceanic and Atmospheric Administration (NOAA). The ANS Task force coordinates governmental efforts dealing with ANS in the U.S. with those of the private sector and other North American interests via regional panels and issue specific committees and work group.

Thank You Ocean Reports Related to Aquatic Invasive Species

Tsunami Debris Hits California; published June 10, 2013:


CA Department of Boating and Waterways – Aquatic Invasive Species  

CA Department of Fish and Wildlife – Aquatic Invasive Program

California Marine Invasives Species Program