Florida’s St. Lucie Estuary received national attention in 2016 as toxic green algal blooms wreaked havoc on this vital ecosystem. A new study contradicts the widespread misconception that periodic discharges from Lake Okeechobee were responsible. Water samples gathered and tested in the year-long study provide multiple lines of evidence that human wastewater nitrogen from septic systems was a major contributor to the high nitrogen concentrations in the estuary and downstream coastal reefs.