Almost 300 loons and other fish-eating birds were found dead at Sleeping Bear Dunes National Lakeshore in Michigan.
The deaths have been attributed to botulism. This bacteria thrives in decaying oxygen-deprived algae mats, which are created when plankton-eating mussels cause the surface water to clear, allowing the sunlight to penetrate deeper in the water. Small fish called gobies travel through the algae mats and pick up the botulism bacteria, which infects the birds that eat the gobies.
Loons are water birds similar in size to a large duck; their defining characteristic is their distinctive call and violent mating dances. The common loon was declared a threatened species in Michigan in 1987.