An invasive South American rodent, the nutria, was discovered in Merced County in 2017, despite having been believed eradicated from the California population. Nutria are continuing to spread across California, with thousands removed since their reappearance.
Over the years, there has been a steady continuation of nutria sightings in California, mostly along the San Joaquin Valley and within Contra Costa County. As of March 2026, 7,841 nutria have been taken in California according to the California Department of Fish and Wildlife.
Nutria are large, aquatic South American rodents that are detrimental to California’s ecosystem, according to the CDFW. The animal was originally brought to the U.S. in 1899 for the fur trade, but failed to reproduce.
According to the California Department of Fish and Wildlife, a nutria’s appearance is described as having a strong resemblance to a native beaver and muskrat. The animal is distinguishable by their “sparsely-haired tails and white whiskers.”
After conducting DNA and genetics testing, CDFW researchers have found a connection between the nutria found in the San Joaquin Valley and a nutria population from central Oregon. Researchers said since the distance between Oregon and California’s Central Valley is significant, the reintroduction of the nutria to California is suggested to be purposeful.
Dr. David Headrick is a professor emeritus in the Cal Poly plant sciences department. For Dr. Headrick, the rate of spread of the nutria is concerning, but there is a rare chance that they will naturally make it to San Luis Obispo’s waterways.
Dr. Headrick wrote to Mustang News in an email that due to the way the Central Valley’s waterways run, they do not flow to the Central Coast; they instead flow to the Bay Area. But, in the off-chance they were to populate San Luis Obispo County, they would find excellent habitats.
He wrote that the nutria’s preferred habitats are land or vegetation along “waterways with creeks, streams and marshy wetlands.” Their presence in the Morro Bay estuary would lead to the grounds being mostly destroyed, along with severe negative effects to Sweet Springs in Los Osos, wetland areas in Pismo, Arroyo Grande and Guadalupe.
“What’s amazing is that humans purposefully introduced Nutria into California a few times for the fur trade,” Dr. Headrick told Mustang News. “Short-sighted greed typically leads to long-term erosion of the environment.”