ELKADER, Iowa — Volunteers were scrambling Thursday to erect sandbag walls around downtown businesses and some homes as the rain-swollen Turkey River threatened to breach protective levees in northeast Iowa.

Authorities said flooding already occurring in Clayton County’s Elkader and elsewhere was expected to worsen as the river was forecast to hit 27 feet Friday morning in Elkader. That’s 15 feet above flood stage and just shy of the record crest of more than 27.75 inches set in 2008.

At just over 15 feet Thursday afternoon, the flooding of low-lying areas was “still manageable,” Elkader City Administrator Jennifer Cowsert said. But, she added, if the level reaches the predicted 27 feet, it’ll flow over the levee.

“When that happens, homes get water in them and the downtown businesses are affected,” Cowsert said.

On Wednesday, officials scoffed at the initial prediction that the river would crest at 25 feet this week, Cowsert said. When that estimate was bumped to 27 feet, Elkader’s fire chief drove upriver to check out the conditions, and came back worried, the administrator said.

“He’s taking their prediction of 27 (feet) fairly seriously,” she said.

After the 2008 flood, local officials launched an effort to buy up the most flood-prone property to keep homes from being built there. Around 20 homes remain in the flood zone, Cowsert said. Even homes outside that zone can expect water in their basements, she said.

Heavy rain Tuesday night and Wednesday morning killed at least one person and forced evacuations and school closures as it washed out roads. The Chickasaw County Sheriff’s Office said Albert Gott, 77, died after his vehicle was swept away by fast-moving water near Lawler.

The Iowa Department of Natural Resources also said Thursday it had received reports from several northeast Iowa cities and a power plant that wastewater treatment facilities had been either completely or partially covered by flood waters, raising the likelihood of floodwaters being contaminated by wastewater, petroleum products and other chemicals washed into the waters. Residents should avoid contact with floodwaters if possible.

Gov. Terry Branstad on Thursday issued a disaster proclamation for Allamakee, Clayton, Fayette, Howard and Winneshiek counties in northeast Iowa. Under the declaration, the counties can use state resources to recover from storms and flooding.