There are several groups of phytoplankton that included diatoms, green algae and blue-green algae. Diatoms and green algae are slightly heavier than water and rely on water current to keep suspended in the water. Some blue-green algae though have the ability to adjust their buoyancy. This means they can sink or rise in the water column as light conditions and nutrients change. Some blue-green blooms are considered toxic and can cause great harm to the lake and animals that drink from the lake during the blooms.
Diatom blooms can color lake waters brown.
This is because diatoms contain brown-colored pigments that mask the green color of the chlorophyll. The term algae bloom is most often applied to describe summer growths of planktonic blue-green algae which may be compromised of circular groups of round cells or clumps of filament. The disintegration of a bloom will release this pigment into the water will color the water temporarily with an intense blue-green or green color. A drastic reduction of the supply of nutrients from the lake's watershed is often the only way to eliminate or even significantly reduce the problems caused by massive algal blooms.