Tiny New Zealand mud snails and a dime. Photo courtesy of the Department of Fish and Game.

NORTH COAST – While quagga and zebra mussels are a major concern for state and local officials, it's another invasive aquatic pest that recently was discovered on the North Coast. {sidebar id=95}

Late last week, Mendocino County Agricultural Commissioner Dave Bengston reported that a biologist conducting a weed survey in the Russian River discovered the tiny New Zealand mud snail.

The snails, which are known to hitchhike on boating equipment and even anglers' boots, have been in California since 2000, according to Bengston's office. This is the first time they've been found in Mendocino County.

Lake County Water Resource Deputy Director Pam Francis said the snails so far have not been found in Lake County.

A full-grown adult mud snail, which is only about one-eighth of an inch long, can multiply into 40 million in a year; as many as 500,000 of them can fit into a single square yard, officials reported.

The California Department of Fish and Game reports that the snails have been found in numerous bodies of water around the state, from Lake Shasta in the north to numerous creeks in Southern California.

They're also in the Yolo County portion of Putah Creek – where they were found in 2003 – the American River, the Lower Napa River and Alameda Creek, Rush Creek in Marin, San Lorenzo River in Santa Cruz and West Antioch Creek in Contra Costa County.

Outside of California, the snails are reportedly wreaking havoc in the Great Lakes, according to media reports.

The snails are believed to be kept in check in New Zealand by a native parasite which isn't present in North America, Fish and Game reported. The snail has no natural predators or parasites and its populations have flourished where they have been introduced; once established, it's believed they can't be eradicated.

Julie Horenstein, an invasive species coordinator with the Department of Fish and Game, said the snails are so tiny that, many times, their numbers have grown very large before they're noticed.

The snails are filter feeders, eating microscopic, one-celled organisms and tiny freshwater shrimp that also are food for fish, said Horenstein. They also reportedly eat algae.

“They're competing with the native animals that eat the bottom of the food chain,” she said.

The question, said Horenstein, is can the snails take enough food out of the food chain that native fish populations would be damaged?

Where the snails found in the Russian River came from is anyone's guess; Horenstein said mollusks can travel long distances even when they're out of water, hitchhiking on fishing equipment, which is a likely way they got to the North Coast. They've also been known to travel in trout brood stock.

The snails tend to frequent creeks and rivers more than lakes, although their find in Lake Shasta leads officials like Horenstein to wonder how significant they could become in a lake setting.

The Lake Shasta find, for Francis, was worrying. “When Shasta found them I knew we were in trouble.”

Earlier this year, the Lake County Board of Supervisors adopted an ordinance to fight invasive species like quagga and zebra mussels. It calls for an inspection program to prevent non-native invasives, and Francis said the mud snails are a pest the ordinance is trying to prevent.

“We had our eye on this,” said Francis.

Keeping boats, fishing equipment, waders, water shoes and toys, and other items that come in contact with water clean, drained and dry is critical to stop the mud snail and the worrisome mussels. “That is the bottom line in preventing the spread of these critters,” said Francis.

Horenstein said to prevent the spread of invasive pests “good hygiene” in dealing with all water equipment is critical, and the Department of Fish and Game is working to get the word out about prevention and the necessity of cleaning boats.

She said people should treat every stream they go to as potentially invaded with exotic, damaging species. (For tips on cleaning equipment, see accompanying story, “Prevent spreading the New Zealand mud snail.”)

Horenstein said there are many more invasive pests beyond the mud snail and zebra and quagga mussels. There also is a disease called viral hemorrhagic septicemia, which causes fish to bleed internally. In addition there are aquatic weeds, which cost millions of dollars annually to address.

E-mail Elizabeth Larson at This email address is being protected from spambots. You need JavaScript enabled to view it..

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