Clean brackish water formed by mixing fresh water and salt water is important to the health of the estuary, but stormwater runoff creates problems when excess rain flows over land, down streets, and through storm drains into the estuary. Paved surfaces prevent water from soaking into the ground, increase the amount of runoff, make it move faster and with greater force, and reduce infiltration to the aquifer. Stormwater runoff can carry fertilizers, animal waste, pesticides, and dirt from pastures and lawns, as well as petroleum and antifreeze residue from parking lots and roads, into the estuary, polluting it. The U.S. Environmental Protection Agency has identified stormwater runoff as the number one pollution source for the nation's waters.