The Free Online Aquaculture Dictionary

Algal Bloom
This picture shows an algal bloom, where the species of algae releases a pigment (a carotenoid) into the water. The colouration of such blooms is the source of the term "red tide" which is also sometimes used to describe an algal bloom. The red pigment is usually released on the death of the bloom as the structure of the algae breaks down and releases the pigment.