Destructive swamp rodents are knocking on the Delta's door. Is it time to panic?

The destructive invasive swamp rodents known as nutria are officially on the doorstep of one of the state's most critically important waterways.

State wildlife officials announced Tuesday that a nutria was killed on agricultural land west of Stockton in San Joaquin County. It's the farthest north the species has been confirmed of the 32 nutria killed so far in California since their discovery in March 2017. The confirmed kill puts the South American rodents on the edge of the Sacramento-San Joaquin Delta.

State and federal wildlife and water officials fear nutria will get a foothold in the Delta's ecologically fragile network of sloughs and rivers. The Delta is the heart of California’s flood-control and water distribution system, supplying water to 25 million Californians and millions of acres of Central Valley farmland.

Full-grown nutria are about the size of a beagle. They can have litters of a dozen or more and become pregnant within 48 hours after giving birth. They aggressively feed on native wetland vegetation, and their burrowing into levees poses a grave risk to the state's water-supply and flood-control infrastructure.

Prior to Tuesday's announcement, nutria were found in Fresno, Merced, Stanislaus and Tuolumne counties. They were first discovered in a private duck-hunting marsh near Gustine in Merced County last year. It is not known how the animals got here.

Eradication efforts are just getting underway. A team of state biologists is being trained how to trap them, and the Department of Fish and Wildlife is working with landowners to get access to private property for trapping. Meanwhile, the state is creating maps and grids to focus their search, said Department of Fish and Wildlife spokesman Peter Tira.

Late last month, Tira's agency was awarded a $1.13 million grant from the Proposition 1 water bond in the hopes of wiping nutria off California's map before they become impossible to eradicate.

Nutria have populated other states after escaping from fur farms decades ago. Louisiana, for example, has spent millions of dollars on bounty and eradication programs with limited success.

Under state law, only land owners or someone working for them are legally allowed to kill nutria, Tira said. There's no hunting program in place for now. Tira said the concern is that it's difficult for untrained hunters to distinguish nutria from native wildlife such as beavers, otters and muskrats.

Biologists ask 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.

Ryan Sabalow: 916-321-1264, @ryansabalow

Related stories from Sacramento Bee