A small west metro lake was the testing ground Friday for a new treatment aiming to kill zebra mussels, the third effort of its kind in the country.

On frozen Christmas Lake, near Lake Minnetonka, crews injected 1,000 pounds of potassium chloride, also called liquid potash, under the ice near the boat launch, where zebra mussels were discovered at the end of the summer. If successful, it will be the first time zebra mussels have been eradicated from Minnesota, and in only the second lake in the country.

The state Department of Natural Resources needed emergency exception approval from the U.S. Environmental Protection Agency and approval from the state agriculture department to use potash, which has been successful in waterways in Texas and Virginia. The chemical kills zebra mussels by cutting off their oxygen, but doesn't affect fish, the DNR says.

Zebra mussels, which have infested hundreds of waterways in Minnesota, quickly proliferate by the millions after entering a lake, often on boats. They clog motors, alter the ecosystem and can be a hazard to swimmers.

On Christmas Lake, experts discovered the infestation at the end of the summer, quickly closed off the area and applied a biological pesticide called Zequanox — the first lake in the country to use it — which killed off the zebra mussels. But more mussels were found outside the area. A copper-based chemical was also used, but the water temperature was too low to use Zequanox, so the DNR applied to be the first Minnesota lake to use potash, and the first frozen lake in the country to use an above-ice application of potash. It cost the DNR $1,500 to treat the 40,000-square-foot area.

If it works, potash may also be tried next spring on Lake Independence, where zebra mussels were found in October. But like Zequanox, potash isn't likely to be a solution for every Minnesota lake and river. Officials say the treatments are too difficult and costly for larger lakes and ones that are fully infested.