I get a lot of questions about weed and algae control in ponds. In fact, this topic is perhaps the most common of all the calls I receive during the spring and summer.
People are concerned about what they consider to be excessive growth of plants in their ponds.
Many people also have submerged, rooted plants of various kinds, but these seem to be of less concern. The nutrients causing this over-fertilization come from a wide variety of organic and inorganic sources. The most obvious, of course, is any lawn or garden fertilizer you may have applied anywhere in the area that might be washed down into the pond. It's amazing how far that fertilizer can travel. Also be sure you know what's happening upstream from you and what your neighbors may be adding to the water.