Few things can ruin a picturesque pond like a coating of slimy moss. Pond moss is unsightly, but it isn't actually moss at all; it's filamentous algae. And like most algae, pond moss thrives in shallow water with high nutrient content due to decomposing plant and animal material or fertilizer runoff. The most efficient natural way to control pond moss is to get rid of its food source. Once that is gone, the pond moss will be gone too.
Physically remove the pond moss floating at the top of the water with a pool skimmer net. In small ponds, this may be enough to stop the spread. By removing the pond moss, you prevent dead pond moss from serving as a food source for a new outbreak. Once you remove the pond moss, dispose of it far from the water to avoid recontamination.
Skim any decaying matter from the bottom of the pond where it collects.
Release beneficial bacteria into the pond. Products like Enviro 4000, Pond Digger or NT-Max contain bacteria that eat decayed matter in your pond. The bacteria are completely natural so they are safe to use in ponds with fish. However, they should never be used in ponds with overflows.
Place a barrier around your pond to prevent fertilizer applied to the surrounding vegetation or septic runoff from running into the water. If either of these is present in your pond's water, they will serve as a highly nutritious food source for pond moss.