The arrival of spring often presents a problem for pond owners as the beautiful, clear green water of their ponds disappears beneath a blanket of lime green, slimy, stinky pond scum. Aquatic algae are primitive plants, having no true roots, stems, or leaves. Pond algae can be found either floating on the pond surface or attached to other plants, bottom sediments or other hard surfaces. Microscopic algae , also called phytoplankton, are tiny, free-floating algae that give the pond water its characteristic green color.
Microscopic algae are the primary producers of dissolved oxygen in pond water.
The presence of a healthy level of microscopic algae in a pond is important for maintaining good water quality and health of the aquatic organisms in the pond, such as fish. A sudden die-off of microscopic algal blooms, caused by a change in water temperature or a stretch of several overcast days, can deplete dissolved oxygen levels in ponds to a critical level for the survival of aquatic organisms. The clue for the pond owner in the control of microscopic algae is to look for a change in the color of the water that might signal that a bloom of microscopic algae is taking place. This color change would be from the clear green water of the healthy pond to a bright, pea-soup green. To quickly check the density of microscopic algae in a pond, nail a light-colored object, such as a coffee can lid or aluminum pie pan, to the bottom of a yardstick.