Algae are microscopic organisms that live in bodies of water and use photosynthesis to produce energy from sunlight. Some algae produce toxins that are stimulated by environmental factors such as light, temperature, salinity, pH, and nutrient levels. These toxins can be released into the water or air and can seriously harm people, animals, fish, and other parts of the ecosystem.
A harmful algal bloom occurs when toxin-producing algae grow excessively in a body of water and becomes visible to the naked eye. Depending on the type of algae that is growing, these blooms can be green, blue-green, red or brown.