Climate Adaptation and Harmful Algal Blooms

EPA supports local, state and Tribal efforts to maintain water quality. A key element of its efforts is to reduce excess nutrient pollution and the resulting adverse impacts, including harmful algal blooms (HABs).

HABs of red tides, blue-green algae, or cyanobacteria can result in severe impacts on:

• Water quality
• Human health
• Aquatic ecosystems
• The economy

Atmospheric changes that lead to higher air temperatures can have a corresponding effect on raising water temperatures.

Higher water temperatures combined with increased stormwater runoff of nutrients can result in conditions favorable for HABs. Consequently, with changing environmental conditions, HABs can occur more often, in more fresh or marine waterbodies, and can be more intense.

An increase in HABs can affect the quality of source water and increase the need for drinking water treatment. HABs may pose a threat to public health through diminishing source water quality. These events can also disproportionately affect individuals with existing respiratory conditions.

HABs sometimes create toxins that can kill fish and other animals. Even if algal blooms are not toxic, they can hurt aquatic life by blocking out sunlight and clogging fish gills. HAB events can also create “dead zones,” areas in water with little or no oxygen where aquatic life cannot survive. Accordingly, an increase in HAB occurrences can adversely affect the effectiveness of ecosystem protection efforts.