Months after a Hollywood flick about those controversial and mysterious crop circles earned a couple hundred million dollars in the United States, a black hole in the ice of a lake near Brainerd has authorities scratching their heads.

The hole was first spotted last February on North Long Lake just north of the central Minnesota resort city and immediately caught the imagination of folks in the area, quickly becoming a source of speculation, conversation and concern.

The Brainerd Dispatch wrote about the hole late last week, summing up the questions in the area: "What caused the hole to appear? Distant earthquakes? New thermal springs on the lake bottom? Sabotage by unknown enemies?"

The area watershed district has since spent $4,000 trying to figure out what's causing the hole, but has yet to find an answer.

While the hole has caused tongue-in-cheek talk similar to that of the crop circles, it also has proven deadly.

The Dispatch reports that as many as a dozen riders of all-terrain vehicles and anowmobiles have gone into the water at the hole, and at least one of them has died.

Signs warning of the hole have been erected around the lake and at public access points.

Such holes aren't uncommon on lakes in the state, but they are typically caused by hot thermal springs being concentrated in one area, but the sudden appearance of the hole last February has many ruling out that possibility.

In addition, Al Cibuzar, head of A.W. Research Laboratories in Brainerd, first viewed the hole while flying over the lake last March. He flew over it again last week and used an infrared, water-penetrating camera and discovered the hole is slowly getting larger.

A diver went through the hole last week and reported "an ordinary lake bottom," the newspaper said.

Researchers plan to continue monitoring the lake bottom, water temperature and other variables involved with the hole.

Another odd wrinkle to the mystery is that the ice thickness on the hole's perimeter ranges from 4 to 10 inches.