Delta News

Why California is freaking out over this invasive giant swamp rodent

In this photo taken on Dec. 13, 2013, a family of young nutria nibble the grass along the shores of Capitol Lake in Olympia, Wash. Nutria, a destructive aquatic rodent native to South America, have invaded the Sacramento San Joaquin Delta.
In this photo taken on Dec. 13, 2013, a family of young nutria nibble the grass along the shores of Capitol Lake in Olympia, Wash. Nutria, a destructive aquatic rodent native to South America, have invaded the Sacramento San Joaquin Delta. AP

A giant invasive swamp rodent known for destroying wetland habitats and damaging levees has invaded the West Coast’s largest estuary that sits on Sacramento’s doorstep.

State biologists report that they’ve found nearly two dozen nutria, a South American aquatic rodent, since March in the Sacramento-San Joaquin Delta. The infestation so far is in wetlands in Merced, Stanislaus and Fresno counties.

The fear is that if the voracious, burrowing plant eaters set up a sustaining population it could mean bad news for the fragile Delta ecosystem and its network of levees, which are vital to flood control and delivering water to farms and cities across the southern half of the state. The rodents also can contaminate water supplies with parasites and diseases that humans, livestock and pets can catch.

Bigger than a muskrat and smaller than a beaver, nutria can grow up to 20 pounds – about the size of a small beagle. They’re prolific breeders and can reach breeding age within six months. One female can produce as many three litters in just over a year – roughly 200 offspring.

Nutria have taken hold elsewhere in the U.S., including in Louisiana, the Chesapeake Bay and the Pacific Northwest. They were introduced to North America in the mid-1900s to supply a fur trade that no longer exists.

California’s last feral population was eradicated from Los Angeles County in 1965, said Peter Tira, a spokesman for the Department of Fish and Wildlife.

It’s not known where the Delta’s infestation originated.

Biologists are asking those who spot signs of nutria to report it online to the CDFW’s invasive species program, by email to invasives@wildlife.ca.gov, or by phone at 866-440-9530.

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