EasyPro Sludge Remover Bacteria Blocks are designed to remove organic sludge from the bottom of lakes and ponds. Sludge is the result of fish waste, dead algae or plant material, uneaten fish food, leaves and other debris. When introduced to the water, the blocks sink, dissolve and begin to remove bottom organic sludge — often several inches per year. Sludge Remover Blocks are great for spot treating around docks, beaches or partially treating large ponds.