From the CBC:

The Great Lakes have faced various threats for years, from industrial pollution to invasive species, but another challenge worries many researchers these days — the emerging chemical threat.

It’s not just pesticides, as scientists are finding worrying levels of pharmaceutically active compounds such as anti-inflammatories, antibiotics, anti-epileptics, and beta blockers in lake water. As well, hormones, pesticides and alkylphenols have been identified as threats. Read more.