Phosphorus is found in fertilizer and in animal
(including human) wastes and is discharged to lakes and rivers
from point (single origin such as a pipe) and nonpoint (diffuse origin such as a field) sources. In the Great Lakes region, we
have reduced point sources by banning the use of phosphorus in
laundry detergents and by limiting the amount of phosphorus which
can be discharged by wastewater treatment plants. Nonpoint sources
can be controlled by managing the way farmers apply manure and
plow their fields to minimize phosphorus runoff to lakes.