According to the California Department of Fish and Wildlife, nutria have extremely destructive feeding habits that often lead to severe soil erosion, in some cases converting marsh to open water. Nutria also burrow into banks and levees, creating complex dens that extend as much as 6 meters deep and 50 meters into the bank, often causing severe streambank erosion, increased sedimentation, levee failures, and roadbed collapses. The rodents, which can weigh more than 20 pounds and are often mistaken for beavers or muskrats, were introduced to California for the fur trade in the early 20th century, but were eradicated by the 1970s. In 2017 a reproducing population was discovered in the San Joaquin Valley and nutria have now been confirmed in Stanislaus, Tuolumne, Merced, and Fresno counties, including an area near Grayson that is only about 25 miles south of the Delta. They could reach the Delta all too easily: A single female nutria can have 200 offspring, which can disperse as far as 50 miles. CDFW has launched an eradication program and is asking the public to report sightings to CDFW’s Invasive Species Program.

Nutria — giant South American rodents—are breeding in the San Joaquin Valley and are on the brink of invading the Delta, where they could wreak havoc, as they have done in Louisiana, Chesapeake Bay and the Pacific Northwest.

According to the California Department of Fish and Wildlife, nutria have extremely destructive feeding habits that often lead to severe soil erosion, in some cases converting marsh to open water. Nutria also burrow into banks and levees, creating complex dens that extend as much as 6 meters deep and 50 meters into the bank, often causing severe streambank erosion, increased sedimentation, levee failures, and roadbed collapses. The rodents, which can weigh more than 20 pounds and are often mistaken for beavers or muskrats, were introduced to California for the fur trade in the early 20th century, but were eradicated by the 1970s. In 2017 a reproducing population was discovered in the San Joaquin Valley and nutria have now been confirmed in Stanislaus, Tuolumne, Merced, and Fresno counties, including an area near Grayson that is only about 25 miles south of the Delta. They could reach the Delta all too easily: A single female nutria can have 200 offspring, which can disperse as far as 50 miles. CDFW has launched an eradication program and is asking the public to report sightings to CDFW’s Invasive Species Program.

About the author

Robin Meadows is an independent science journalist in the San Francisco Bay Area. She covers water and climate change adaptation for Estuary News, is the water reporter for the Bay Area Monitor, and contributes to Bay Nature, Frontiers in Ecology and the Environment, PLOS Research News and Water Deeply. Robin also enjoys hiking and photography.