Boaters planning a jaunt on the St. Croix River for the Fourth of July likely will be forced to take it slow, after a no-wake zone was put into effect Wednesday by the Minnesota Department of Natural Resources (DNR).

The river topped 683 feet at the Stillwater gauge on Wednesday, triggering the no-wake zone from Taylors Falls to where the St. Croix meets the Mississippi River at Prescott, Wis.

It is expected to remain in effect at least until next Thursday's holiday, said Cmdr. Jerry Cusick of the Washington County Sheriff's Office, who heads the agency's boat patrol. The river has risen more than 3 feet since Sunday at Stillwater. "And we got dumped on again today," Cusick said Wednesday.

The no-wake zone means boats can only go fast enough to maintain the ability to steer in the water, usually not more than 5 miles per hour. The fine for violating the zone is $140.

From the Namekagon Dam in northwestern Wisconsin to Prescott, the St. Croix River is unusually high and flowing fast, and the water is cold due to heavy early summer rains in the region, according to the National Park Service.

Over the weekend, rising water hit the "action stage" level, putting local authorities on alert for the possibility of flooding. "This is pretty abnormal for summer," said Deborah Paige, director of emergency management with Washington County. "We typically see this in the spring."

The latest forecast put the river level at 684.2 feet on Tuesday. Flood stage is 687 feet, and the Stillwater Lift Bridge would close at 686 feet.

Along with watching the St. Croix, rising water on the Mississippi River is being monitored as well, Paige said. An island off Lions Levee Park in St. Paul Park that serves as a flood bellwether is now submerged, so the forecast is being closely watched, she said.

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