LA CROSSE, Wis. - Emergency workers in La Crosse have recovered the body of a college student from a car that broke through the ice on a creek.

Police say Winona State University student Ellen Ahmann of Woodbury was the lone occupant of a four-door vehicle that broke through ice on Swift Creek just south of downtown, La Crosse police said Thursday morning.

Investigators don't yet know when the 21-year-old Ahmann drove onto the ice. A La Crosse Municipal Transit Utility bus driver called police at 1:27 a.m. Wednesday when he noticed tire tracks in the snow leaving Jackson Street, heading over an embankment towards the water.

The vehicle plunged down a 40-foot embankment but the ice didn't immediately break. The vehicle headed a little south on the ice before falling through into the water.

Dispatchers paged members of the La Crosse Dive Unit about 1:30 a.m., when it was already too late to save the driver, unit commander Shawn Mahoney told the LaCrosse Tribune.

Emergency personnel from multiple agencies began the recovery mission about 9 a.m. Wednesday in frigid temperatures. They widened the hole made by the car before a diver underwater for about 10 minutes hooked straps to its axles and a tow truck pulled it from the creek about 1 p.m., Mahoney said.

The dive unit trains annually in Swift Creek, where water temperatures were about 34 degrees Wednesday, he said.

An autopsy planned for Friday in Madison will determine how Ahmann died and whether alcohol or drugs were involved.