Lake Kanasatka, a scenic 352-acre lake near Moultonborough, New Hampshire, was once renowned for its clear, pristine waters. By 2020, however, residents and visitors were shocked to see the lake turn a bright, neon green—similar to Gatorade. The cause: cyanobacteria, a rapidly spreading algae that can produce toxins harmful to both humans and animals. These blooms are fueled by nutrient pollution—runoff containing phosphorus and nitrogen from septic systems, lawns, and roads.

Recently, warming waters caused by climate change have made these outbreaks more intense and frequent, turning once-healthy lakes into dangerous ecosystems. Facing declining water quality, health advisories, and dropping tourism, the Lake Kanasatka Watershed Association decided to take drastic steps. In 2024, they used a last-resort chemical treatment to eliminate the algae and try to restore the lake’s health. This episode explores what caused the crisis, why the chemical treatment was controversial, and—most importantly—whether it succeeded in saving Lake Kanasatka from ecological collapse.