About 200 National Guard troops will be on active duty in the Moorhead area Thursday to help combat flooding officials called "very dangerous."

Gov. Mark Dayton declared a state of emergency in 46 of Minnesota's 87 counties due to high water along the Mississippi, Minnesota, St. Croix and Red Rivers.

The declaration also triggers an effort to have the federal government pick up a substantial part of the tab for flood damages. Minnesota must first demonstrate $6.5 million in damages statewide, a figure that Wade Setter, deputy director of the Homeland Security and Emergency Management division of the Department of Public Safety, said may have already been reached.

At Fargo, across the Red River from Moorhead, about 1,000 high school students pitched in with last-minute sandbagging in the face of a crest expected to reach between 39 and 41 feet Sunday. Also Wednesday, officials indicated the Stillwater Lift Bridge, a key commuter link for east metro residents, will be closed Friday morning, or possibly earlier, due to a second rise on the St. Croix River. City workers and jail inmates were reinforcing a temporary levee with additional plastic and sandbags Wednesday.

"This is a very dangerous situation. There's a lot of water moving through very fast," Setter said. "It doesn't always look as dangerous as it really is."

In Washington County, river communities are in watch-and-wait mode, said Deb Paige, the county's emergency management director. "This may be a longer flood season than normal, and we're kind of getting ready for that," she said.

Late Wednesday afternoon, the St. Croix River level was at 86.01 feet, rising nearly 3 inches since midnight. The National Weather Service says it will hit 87 feet early Saturday.

On the Mississippi, two areas of concern are an aging levee in Newport and a bridge to Grey Cloud Island Township. John Neska, Newport's assistant superintendent for public works, said officials are watching forecasts closely.

"Hopefully,'' he said, "the sun keeps shining."

Staff writer Kevin Giles contributed to this report. mcaul@startribune.com • 612-673-7646 jeanderson@startribune.com • 651-735-0999