Invasive Nutria Rodents Threaten Bay Area Infrastructure, Water Supply, and Public Health
A large, invasive rodent known as the nutria, which can weigh double the size of a cat, is raising alarm across the Bay Area as its population expands. The nutria poses serious threats to infrastructure, California’s water supply, and the health of humans, pets, and livestock.
Nutria, native to South America, were first brought to the U.S. in the late 1800s as part of the fur trade and introduced in Southern California. These semi-aquatic rodents are often mistaken for beavers or muskrats and are commonly called swamp rats. They can grow up to 25 pounds and measure around 2 feet in length, not including their tails. A key distinguishing feature of nutria is their bright orange teeth.
Although California had eradicated nutria in the 1970s, a reproducing population was discovered in the San Joaquin Valley in 2017, according to the California Department of Fish and Wildlife (CDFW). Since then, CDFW has worked to prevent the infestation from spreading. In 2024 alone, over 1,100 nutria have been trapped and killed, with nearly 5,200 eradicated since 2017. The rodents have now been found in Contra Costa and Solano counties.
In California, nutria are classified as a nongame mammal, allowing property owners to kill them to protect crops and property. However, there are legal restrictions on the types of traps used. Krysten Kellum, a CDFW information officer, emphasized that eradication efforts involve humane euthanasia through the use of pellet pistols. Poisons and pesticides are not used.
Nutria are known for burrowing, often creating habitats in embankments, dams, and dikes, leading to severe erosion and damaging critical waterways, levees, and road infrastructure. Their feeding habits also pose a risk to wetland ecosystems, where they threaten endangered species and destroy vegetation. Nutria consume up to 25% of their body weight daily in plants but waste much more, causing damage to crops and the native plant community.
Additionally, the rodents are a public health risk. They can carry and spread bacteria and parasites, including tuberculosis, septicemia, and tapeworms, which pose threats to humans, livestock, and pets. They can also contaminate water supplies and cause skin rashes known as “nutria itch.”
To prevent further infestation, the CDFW has called on residents in affected areas to grant access to survey teams for trapping efforts. Survey teams have been deployed across the Delta, including Contra Costa and Solano counties. The agency has also set up cameras in the Delta to monitor nutria populations.
Merced County has seen the highest number of nutria captured, with over 2,500 removed since 2017. In the Bay Area, 486 nutria have been killed in Solano County, and two have been found in Contra Costa County as of this week.
Contra Costa County officials are working with state wildlife agencies to stop the spread. The county’s agricultural commissioner, Matthew Slattengren, warned that nutria could easily spread to other regions via the Delta, posing further threats to wetland habitats, crops, and levees.
Nutria populations grow rapidly, as females can produce their first litter at just eight months old and can breed year-round. Litters typically range from two to 13 pups, with three litters produced annually.
Officials urge residents who spot nutria to photograph them and report the sighting to wildlife officials by emailing Invasives@wildlife.ca.gov or calling (866) 440-9530. They warn against releasing captured nutria and advise contacting local CDFW offices or agricultural commissioners for assistance.
