Weird hole in frozen lake ice

In December, 2001 residents of Brainerd, Minnesota noticed a hole in the thick ice covering North Long Lake. The hole was one-half mile long by 400 feet wide, with a depth of 24 feet. The rest of the lake was covered with ice 18 inches to 3 feet thick. No explanation was found for the hole that remained unfrozen all winter. In November, 2002 the hole showed up again. In January, 2002 the Minnesota School of Diving sent divers to collect water from the hole and also to use dye to observe the currents inside the hole. Tests have revealed no answers. The only differences found were that the water was warmer than the surrounding water, the iron content was higher and the water in the hole had a greener color. See earthfiles.com for the complete story. Any thoughts what could cause this?

Who knows...looks like..that GLobal Warming........................

Could be a hot spring of sorts, water is heaviest at 33 degrees F, it then sinks to the bottom, if the lake is domed shaped, it would create a towers flow of slightly warmer water being pushed up by a gass leak, minor volcanic activity, something small because the cold water is keeping the water reletively neutral. But, who knows I am merily guessing here.. very strange though.

Probably some geo thermal event underneath the hole.

No that just a sexy hole.

It's HOT!

That's why.

Could be a high concentration of fish or types of fish living in the water changing electrical wave lengths causing differences in the amounts of energy produced as heat maybe just takes a degree to prevent freezing.

Probably a new spring opened up can't think of anything else that would do it