Snohomish County authorities raised the death toll to 24 in the mudslide that buried about a square mile on the Stillaguamish River last week.
As of Monday morning, officials had identified 17 of the 24 victims.
Search crews believe 22 people are still missing in the mud, up to 4 feet deep in spots, that blocked a highway and dammed a river.
Meanwhile, volunteers searching the mud are encountering toxic sewage, household solvents, gas, oil and other hazardous substances, said Steve Harris, division supervisor for the eastern incident management team in Darrington, Wash.
At the end of each day, search crew members and any personal affects they find in the debris must be decontaminated. Officials are concerned about possible incidents of dysentery and tetanus.
[Snohomish, Wash., County]