Todd Matthies, Tim Moe and Pat Krueger, all of the Minnesota School of Diving in Brainerd, videotaped and photographed the bottom of the lake under the hole, which measures about 2,000 feet long by 400 feet wide on the Highway 371 bay.

"Saw a few fish, some snails, weeds, pretty typical stuff so far," said Matthies, the first diver to investigate the hole.

Matthies put a dye in the water that enables a camera to detect currents flowing through the hole.

"It didn't seem to move much," Matthies said of the dye. "But it's hard for me to determine that. We need to analyze the film."

The other divers measured water temperature, dissolved oxygen, pH content and conductivity.

Wednesday's operation was observed by a dozen lake residents, as well as area and Twin Cities media. Coffee and doughnuts were served at the lake access by the Thirty Lakes Watershed District.

The Crow Wing County Sheriff's Department had a Hovercraft on hand for emergency rescue. But the only rescue it made was of a portable fish house that had been set up as a warming house for the divers. A gust of wind caught the house and blew it onto the black hole.

But the thin layer of ice covering the hole prevented the fish house from becoming the hole's 13th casualty.