The Great Lakes, which hold 20% of the world’s surface freshwater, could become hazardous for drinking with the development of Harmful Algal Blooms. Dr. Gabriel Filippelli, Director at the Center for Urban Health, Professor in the Department of Earth Sciences at the Purdue School of Science in North Blackford, Indiana USA, tells us what tests are revealing about the toxins in the algal blooms, what causes these blooms, and what impact this is having on our Great Lakes.