What are they?

Algal blooms occur when the proper conditions are met for a colony of algae to rapidly increase in populations. These blooms usually are green, yellowish-brown or red. Bright green blooms occur as the result of blue-green algae which are actually bacteria.

Algae blooms are caused by a combination of environmental factors including available nutrients, temperature, sunlight, ecosystem disturbances, hydrology, and the water chemistry.