SNOHOMISH, Wash. (AP) — A dike breach in a dairy waste lagoon with a 21-million-gallon capacity has sent a large amount of cow manure flowing through farm fields and into the Snohomish River, the state Agriculture Department said Tuesday.

A 30-foot-wide section of the dike failed either late Sunday or early Monday, agency spokesman Jason Kelly said. The department said the manure filtered through fields and into French Slough, which carried it into the river.

The Washington Health Department said it appears no public drinking water supplies have been affected. The Snohomish Health District is urging people to avoid the river, since cow manure is likely to contain E. coli bacteria.

The state's Fish and Wildlife Department is assessing impacts on fish. No fishing season is currently open on the Snohomish River.

The dairy, Bartelheimer Brothers, is cooperating in efforts to prevent further pollution. The farm has 750 dairy cows and grows 600 acres of corn and hay for cattle feed.

"We're doing everything we can to respond to this lagoon failure," Jason Bartelheimer said. He added the farm is using its additional manure storage capacity in an effort to prevent further runoff into the slough.

The dike enclosing the 580-foot-diameter lagoon is 15 feet tall, and the lagoon bottom is 5 feet below ground level. The breach drained the lagoon of all its contents above ground level. However, it was unclear how much manure was in the lagoon, and the Agriculture Department did not estimate how many gallons spilled.

Kelly said the lagoon was built in 1997 to the standards of the U.S. Agriculture Department's Natural Resources Conservation Service.

Kelly said the dairy's latest manure management inspection, conducted by the state Agriculture Department in April 2009, showed "only minor issues that were subsequently addressed."

Representatives of the Conservation Service and the state Ecology Department are trying to determine why the lagoon failed.

Also, read "Big manure spill at dairy flows into Snohomish River" from The Seattle Times.

Copyright 2010 The Associated Press.