‘Boy, they’re an ugly-looking thing’: Voracious swamp rodents swarming California and endangering water supply

‘The way they multiply – jeez,’ says almond farmer

A remote camera image shows nutria in Merced County, California, in 2018 (AP)

Voracious swamp rodents have invaded parts of California, endangering the state’s water supply and threatening to destroy the habitats of other animals.

The nutria, resembling something between a large rat and a beaver, can weigh up to 9kg and consume up to a quarter of that mass daily in riverbank plants. Their destructive burrowing can damage wetland habitats.

“Boy, they’re an ugly-looking thing,” said David Passadori, an almond and walnut farmer in central California. “And the way they multiply – jeez.”

The nutria, known elsewhere as the coypu, was thought to have been eradicated in the 1970s. It was first brought to the region from Latin America by fur traders in the 19th century.

Most of the female nutria that wildlife rangers have found so far have been pregnant, and the animals can have up to three litters a year. More than 700 animals have been killed by rangers since their return was detected in 2017.

One of the greatest threats posed by the nutria is to public safety, officials have said. Unchecked, they could break into the Sacramento-San Joaquin river delta in central California, which provides drinking water for some 10 million people, as well as irrigation and flood protection.

“It sounds ridiculous, but these swamp rats are actually a major problem for our water infrastructure. They can cause floods by destroying irrigation canals and levees,” said Democratic congressman Josh Harder earlier this year.

Now, armed with $10m (£8m) in state funds, rangers are deploying new tactics to eradicate the nutria and try to prevent the widespread destruction they are known to cause.

“Over the past two years, our best efforts were trying to not even control the population but keep it from exploding while we pursued the resources needed to actually pursue eradication,” said Valerie Cook, from the California fish and wildlife department’s eradication programme.

“We haven’t had nutria in California for 50 years, so nobody really knows much about them,” Peter Tira, a department spokesman, said. “We’ve had to learn on the job as we go.”

Farmers, landowners and biologists in the Central Valley, an agricultural region 130 miles north of Sacramento, have been on high alert. The area is the US’ most productive agricultural region, responsible for more than half its fruit, vegetables and nuts, including almost all apricots, table grapes, carrots, asparagus and tree nuts.

Damage to the region, whose output was estimated in government figures to have been $29bn (£23bn) in 2017, would be disastrous for its economy and diet.

“It would mean no more sushi, because the alternative would be to buy rice from Japan or Korea, where the price is five times higher,” said Daniel Sumner, director of the Agricultural Issues Centre at the University of California-Davis. “Kiss off carrots, or live without table grapes in the summertime.”

Additional reporting by Associated Press