Algal or Algae bloom A bloom is a rapid increase or accumulation in the population of algae in fresh or marine water systems, and is often recognized by the discoloration in the water from their pigments such as red, blue green and golden). The term algae encompass many types of aquatic photosynthetic organisms, both macroscopic, organisms like seaweed and microscopic, unicellular organisms like cyanobacteria. Algal bloom commonly refers to rapid growth of microscopic, unicel