Filamentous algae (the fuzzy or stringy kind) is a beneficial type of algae that harbors good bacteria necessary for clearing the water. The trouble with this type of algae is it is unsightly when it grows long in the streambeds, waterfalls, and along the sides of the pond. A short layer is good for the pond, but when it grows to two or more inches, it is often considered to be too much. Fish will usually take care of the string algae in the pond itself. On the waterfalls and streams, hand weeding removes the longest parts sufficiently if done every couple of weeks. Several products including algaecides, barley straw, or barley extract promote string algae control if used on a regular basis. Also, pH should be checked when there is an excess of string algae. If pH is too high (over 7.5 or so), the bacteria that generally would out-compete the algae for the nutrients in the water will not grow properly.