Total suspended solids (TSS) are the portion of fine particulate matter that remains in suspension in water. TSS is measured by weight, usually as milligrams per liter (mg/l). Particulate matter larger than 2 microns is considered a suspended solid. The majority of suspended solids are made up of inorganic materials; however, bacteria and algae can contribute to total solid levels. These suspended solids include anything floating through the water such as gravel, silt, sand or clay. Another contributor to TSS is the decomposing of plants and animals, which results in small particles breaking away from the organism becoming a suspended solid in the water.