I don't know what it is, the pond id otherwise perfect. The water is perfectly clear, great balance of plants and fish. A "pond guy" told me it was a mold or fungus but did not know a name or have a solution. Anyone else have any Ideas? It looks like a fresh layer of snow, just a light dusting as some rocks are visible through it. It is about 4'x4' in diameter in a 8,000 gallon pond. In the area it is in the water is about 8"-10" deep, it is just down stream from the bog, the water flow is minimal about 2000 GPH, and it is under a bridge (shady). But I have seen it before in another pond and it was in full sun at that place.