Planktonic algae are microscopic free-floating cells suspended in the water column. This population of cells is generally composed of green and blue-green alga. Water discoloration from green to brown commonly occurs from free floating cells.

Severe blooms create a rust red, green or brown paint-like film on the water. Densities can fluctuate from a minor dusting to a pea soup several feet thick.

Control can be obtained on most species but safety factors should be weighed. The large volume of water occupied by cells can impact dissolved oxygen levels. Potential for a fish kill is increased when these cells die off suddenly from natural causes.