Decomposition in pools, ponds, and lakes takes place mostly in the benthic zone.
The benthic zone is the region at the lowest part of water bodies such as lake, stream or ocean which include the floor, the sediment surface and some sub-surface layers. Decomposition mostly occurs in the benthic zone. The benthic zone contains mainly aquatic macro-invertebrates (benthos) such as insects, worms, beetles, clams, and mites which breakdown organic matter that are suspended in the water.