California's Nutria Invasion Likely Caused by Intentional Reintroduction

Genetic analysis suggests the state's current nutria problem stems from animals transported from Oregon

Apr. 9, 2026 at 8:34pm

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A highly structured abstract painting in soft, earthy tones featuring sweeping geometric arcs, concentric circles, and precise botanical spirals, conceptually representing the complex natural and human factors behind the spread of the invasive nutria species in California.An abstract visualization of the complex biological and ecological forces driving California's ongoing battle against the destructive nutria invasion.Gustine Today

California has been battling a resurgence of the destructive 20-pound rodent known as nutria, and wildlife officials now believe the current invasion was likely caused by someone intentionally reintroducing the species to the state. Genetic sequencing has revealed the nutria populations are most similar to those in Oregon, suggesting the animals were transported from there, rather than migrating on their own.

Why it matters

Nutria pose a serious threat to California's fragile wetlands and endangered species, as well as crops and infrastructure like levees. The state spends around $5 million annually on eradication efforts, underscoring the significant environmental and economic impact of this invasive species.

The details

In the late 19th and early 20th centuries, nutria were bred worldwide for their fur, and were first imported to Oregon in 1937. After feral populations flourished, eradication campaigns led to the rodents being pronounced eliminated from California by the 1970s. However, in 2017, a pregnant female nutria was discovered in Merced County, sparking the current battle against the species' resurgence.

  • Nutria were first imported to Oregon in 1937.
  • Nutria were pronounced eradicated from California in the 1970s.
  • A pregnant female nutria was discovered in Merced County in 2017, reigniting the state's battle against the invasive species.

The players

Greg Gerstenberg

A senior biologist with the California Department of Fish and Wildlife.

Michael Buchalski

The Fish and Wildlife wildlife genetics research lead.

Valerie Cook

The Nutria Eradication Program Manager.

California Department of Fish and Wildlife

The state agency responsible for managing California's wildlife and natural resources.

California Department of Food and Agriculture

The state agency that operates vehicle inspection stations to prevent the importation of invasive species like nutria.

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What they’re saying

“Given where nutria were rediscovered in California, it is nearly impossible that they could have migrated there on their own. It's too far of a distance and we don't find any nutria in the areas in between. That makes human introduction the most likely scenario.”

— Michael Buchalski, Fish and Wildlife wildlife genetics research lead

“This study supports our long-held belief that the current invasion is the result of reintroduction rather than explosive growth of a remnant, undetected population. While we can only speculate on the 'reasoning' behind the reintroduction of this incredibly destructive invasive species, these findings highlight the critical importance of biosecurity inspections aimed at preventing the importation and transportation of invasive plants and animals into and within California.”

— Valerie Cook, Nutria Eradication Program Manager

What’s next

The California Department of Fish and Wildlife and the California Department of Food and Agriculture will continue their efforts to eradicate the nutria population and prevent further introductions of the invasive species.

The takeaway

The discovery that California's nutria problem was likely caused by intentional reintroduction highlights the critical need for robust biosecurity measures to prevent the importation and spread of destructive invasive species. This incident underscores the significant environmental and economic toll that can result from such actions, and the ongoing challenges faced by wildlife officials tasked with protecting the state's fragile ecosystems.