Free-floating algae are the most common cause of green pond water. Blooms of algae in ponds are a sign of an unbalanced system. Imbalances can be caused by past landscape management decisions and current inputs of lawn fertilizers, grass clippings, or pet waste. Fish waste also can contribute to algae blooms; too many fish stocked in a pond can overload the system. Healthy stormwater ponds reduce flooding and help prevent pollution downstream. They can also be a valuable urban oasis for birds and other wildlife. To protect your neighborhood pond, maintain a 10-foot fertilizer-free and no mow buffer from the water’s edge; blow grass clippings back into yards and not down storm drains; and pick up after your pets promptly.