We first investigated this to solve an algae problem in our pond, caused in part by runoff from surrounding development. Feeding on the fertilizers entering the water, the "algae blooms" use up the oxygen in the water, reducing the water quality for animal life. The islands are made of a polymer matrix that is seeded with phosphate-eating microbes. This naturally reduces the nutrient level, removing the excessive algae growth without chemicals. In addition to reducing algae, the islands provide shade to fish and other aquatic animals, as well as a safer nesting area for ground-nesting birds (as two geese have already discovered).