Botulism intoxication, which causes the paralysis and death of intoxicated vertebrates, is caused by ingestion of neurotoxins produced by the bacterium Clostridium botulinum. Periodic outbreaks of type E botulism have resulted in die-offs of fish and fish-eating birds in the Great Lakes since at least the 1960s, but outbreaks have become more common and widespread since 1999, particularly in lakes Michigan, Erie and Ontario (Riley et al. 2008). Botulism has been responsible for over 80,000 bird deaths on the Great Lakes since 1999, and extensive bird mortality in northern Lake Michigan near Sleeping Bear Dunes National Lakeshore (SLBE; over 4150 birds in 2007) received widespread press attention and caused great public concern. The actual sites of toxin exposure for birds remain unknown. (via USGS Great Lakes Restoration Initiative - Habitat & Wildlife - Avian botulism in distressed Great Lakes environments)
Type E botulism is not an invasive species and has been present in the Great Lakes system for many years. However, the recent trend of warmer winters has led to more outbreaks. If lake water does not cool enough in the winter, the bacteria are able to start reproducing and this causes problems for birds (especially waterfowl), fish species, and mud puppies. According to an expert who gave a seminar at my college, another outbreak is expected this year.