Algal Bloom

You may often see it as "polluted water" underneath roadways or in canals, but Algal bloom aka marine/water bloom is a major increase in Algae in a system, sometimes in fresh water composed of phytoplankton which produce harmful toxins called HABs.

Also, not very many plankton are involved in the blooms. When there is a high density of colored cells, the general color of the bloom will change allowing for recognition.

The most common colors are green (light or dark), brown, or red. The concentration of algae is very high during a bloom. Sometimes, there are up to 1,000,000 cells of algae per one millimeter. This poses a threat to wildlife because of the negative biological impact.

Some blooms are created by the release of phosphorus and nitrogen into the waters, causing the growth of algae. Because of the rapid growth of Algae, it causes other plants and Algae to die.

Website: http://www.sciencedaily.com/articles/a/algal_bloom.htm
Picture: http://plants.ifas.ufl.edu/manage/sites/default/files/01_algae_07.jpg