HELENA - Two windmills at a Rocky Mountain lake are powering aerators to help sensitive westslope cutthroat trout survive the winter.

As the windmill blades turn at Wood Lake on the Rocky Mountain Front west of Great Falls, air moves through a hose and then through a device that diffuses the air, producing the kind of bubble effect seen in home fish tanks. This gives the fish oxygen to help them survive while ice covers the lake.

The aeration creates, in the ice, a hole that allows the escape of gases from decomposing lake vegetation. Absent the opening, available oxygen in the water could be used up and the trout would die, the Montana Department of Fish, Wildlife and Parks said.

Fish kills have occurred at Wood Lake in some previous winters, and are of particular concern at small bodies of water. Wood Lake goes to a depth of only about 10 feet. Its surface covers 20 acres.

The windmills, resembling those traditionally seen on farms, were installed last month and came from Canada's Koenders Windmills Inc. Windmills are new to Wood Lake but have been widely used elsewhere.

Koenders alone sells more than 6,000 a year, mostly in North America, marketing manager Doug Hicks said from Kelowna, British Columbia. Prices range from $1,000 to $2,000.

The two windmills at Wood Lake likely will be removed late this winter or early in the spring, said Dave Yerk, a fisheries biologist for Fish, Wildlife and Parks. Meanwhile, the agency is warning snowmobilers and winter anglers about the perils of thin ice and open water while the windmills function.

Yerk said westslope cutthroat trout planted at Wood Lake within the last couple of years appear to have thrived.

Environmental group American Wildlands first sought federal endangered species protection for the fish in 1997. That and subsequent requests to the U.S. Fish and Wildlife Service were denied.

On the Net:

Fish, Wildlife and Parks: www.fwp.mt.gov

Koenders Windmills Inc.: www.koenderswindmills.com