Harmful plumes of algae in waterways have been much in the news lately, in California and nationally. We talked to James Cloern, a senior scientist at the US Geological Survey and a member of the PPIC Water Policy Center’s research network, about this pressing water quality issue. PPIC: What are algal blooms, and how big a problem are they for California? James Cloern: Our waterways are home to many thousands of species of microscopic algae, but only a few dozen can develop into harmful blooms.