Wastewater may be conveyed in a sanitary sewer that conveys only sewage. A combined sewer carries both domestic sewage and stormwater. Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. They can become concentrated in sewage sludge. Soybeans grown in sewage sludge likely contain elevated concentrations of metals. Currently, only sewage and effluent from fish ponds run in the river's channel. This avoids mixing digested sludge with incoming sewage. Vermicomposting can also be applied for treatment of sewage sludge. Some cattle raised in the United States feed on pastures fertilized with sewage sludge. This aims to reduce the amount of pharmaceutical waste that gets into sewage and landfills. The corporation is also responsible for waste disposal and sewage management. A phytoplankton study found high nutrient concentrations linked to sewage effluents. Increased nutrient levels can be a result of sewage or chemical fertilizer runoff. The species lives in stagnant water, such as sewage and lagoons. Sea water is used for sewage lines.