A toxic red tide has returned to the San Francisco Bay Area, nearly one year after an unprecedented algae bloom killed thousands of fish and marine life in the region. Citizen scientists near the Berkeley Marina reported seeing discolored water Friday; various groups then went out to collect samples and had them analyzed, according to David Senn, a scientist at the San Francisco Estuary Institute. … Wastewater disposed in large bodies of water can result in high amounts of nitrogen and phosphorous, which can drive the growth of algae blooms. The San Francisco Bay has 37 wastewater treatment plants that serve millions of people in the region.