The water clarity in Lake Itasca has been steadily declining for years. Nutrients that can feed harmful algae blooms and turn the water a sickly green are unusually high for a lake of its size and pristine location.

Minnesotans have done everything they can to protect this picturesque lake in an ancient woods from which the country’s great river begins. But Lake Itasca’s chemistry, shallow depth and even its unusual wishbone shape may make it particularly vulnerable. With higher temperatures in northern Minnesota allowing less ice, the lake is receiving more sunlight and a longer growing season.