AGUACYCLE
Issue explainer

Harmful Algal Blooms and Source-Water Quality

Nutrient pollution and warming water are fueling toxic algae outbreaks that can shut down drinking-water intakes — as Toledo learned in 2014.

Harmful algal blooms (HABs) occur when nutrients — mostly nitrogen and phosphorus from farm runoff, sewage, and lawns — combine with warm, slow water to trigger explosive algae growth. Some blooms release toxins dangerous to humans and animals.

In 2014, a bloom on Lake Erie forced Toledo, Ohio to warn half a million people not to drink their tap water for days. Blooms now affect lakes, rivers, and reservoirs nationwide, threatening the source water utilities depend on.

Reducing nutrient runoff is the long-term fix; in the meantime, utilities invest in monitoring and advanced treatment to keep toxins out of finished water.

Sources & further reading