Large rodents native to South America, nutria began causing alarm along rivers and other waterways after being rediscovered in California in 2017.

Most concerning, nutria have the potential to damage levees and tidal wetland restoration sites in the Sacramento-San Joaquin Delta, California’s water hub, from their extensive burrowing and voracious appetites.

Nutria strongly resemble beavers, but with arched backs and long, round, sparsely haired tails. Adults typically reach a body length of 2 feet and can weigh as much as 20 pounds. With their webbed back feet, nutrias are strong swimmers. They reproduce quickly and can consume as much as 25 percent of their body weight in plant material each day. Even newborns may swim and eat vegetation on their first day. Because of nutrias’ feeding habits, as much as 10 times the amount of plant material consumed is destroyed, according to the California Department of Fish and Wildlife.

Nutria were originally introduced in 1899 to the United States at Elizabeth Lake in northwest Los Angeles County for the fur trade, but failed to reproduce, according to the Department of Fish and Wildlife. Subsequent introductions were successful, as records indicate nutria were present in the Central Valley and South Coast of California in the 1940s and 1950s.

California had licensed nutria farms but when the fur market collapsed, some of those farms were abandoned. Recognizing the damage nutria could cause, the California Department of Food and Agriculture undertook eradication efforts that removed nutria entirely by the 1970s.

Nutria have since been discovered in San Joaquin, Stanislaus, Merced, Fresno, Mariposa and Tuolumne counties. In May 2019, a nutria was detected near Rough and Ready Island, on the east side of the Sacramento-San Joaquin Delta, near Stockton. That was about 16 miles north of the nearest known population and previous detections, according to the Department of Fish and Wildlife.

The department began working with state and local agencies to eradicate nutria in the most effective manner. As of May 2020, Fish and Wildlife reports 1,078 nutria were killed. 

The Department of Fish and Wildlife notes that there is a small window of opportunity to successfully eradicate the population of nutria from California because as the population size and geographic area of infestation increase, the probability of successful eradication decreases, and California would be left to manage and mitigate the devastating impacts of nutria.