algal bloom

An algal bloom is a sudden population explosion of algae in a lake, river, or coastal water, turning it green, red, or brown almost overnight. Blooms are fueled by excess nutrients, typically nitrogen and phosphorus from fertilizer runoff and sewage, combined with warm, still conditions. Their consequences for food and water safety are serious: some bloom-forming cyanobacteria produce toxins that contaminate drinking water and accumulate in shellfish and fish, while the decay of massive blooms depletes oxygen and kills aquatic life. Monitoring programs test water and seafood during bloom seasons, and closures of shellfish beds protect consumers from algal toxins that cooking cannot destroy. Reducing nutrient runoff at the source remains the fundamental prevention strategy.