Water that does not infiltrate the
soil runs off across the surface of the watershed. Runoff begins
as a sheet of water and then turns into small trickles and then
streams. Runoff may contribute water directly to lakes or it may
flow first to steams (streamflow) and then to lakes or the ocean.
Runoff can erode the land surface, leading to
pollution of lakes and rivers. If precipitation is intense and/or
the soil is saturated, flooding can occur. Watershed managers try
to reduce erosion and flooding by using good land use practices
and by building control structures.