Lagoons can be dredged to remove biosolids, alum, ash, sediment, or other sludge.  Dredging of lagoons usually utilizes hydraulic dredging to pump the sludge for dewatering and disposal purposes.  Lagoons are often a treatment for water quality to remove any contaminants, organic matter, or pollutants prior to discharge, reuse, or land application.  If the lagoon loses enough capacity its function may diminish.  Dredging can restore the function even by removing the sludge, often while the lagoon is still in use.