Humans affect the phosphorus cycle mainly by the use of fertilizers and raising livestock, especially hogs. Fertilizers and hog waste are high in phosphorus, which makes its way into the soil (where it is necessary in moderate amounts) and, due to runoff, in water. Another factor is in the use of detergents, many of which contain sodium tripolyphosphate, or STPP. The phosphate in STPP, the use of which has been severely curtailed due to environmental regulations, can lead to algal blooms in water, which can kill fish and other plants. It is by these activities that we alter the phosphorus and, in reality, the nitrogen cycle as well.