A watershed is an area of land from which rain and melting snow
drain into a river, stream, or other body of water. A watershed may be small, like the land that drains
into a neighborhood stream, or large, such as all the land that drains into a large river. Large
watersheds are made up of many smaller watersheds.
In addition to the lakes, rivers, streams, and other surface waters,
watersheds include all the water that soaks into the ground and
becomes part of the groundwater. Groundwater fills the spaces
between rocks and soil particles underground in the same way that
water fills a sponge. Groundwater slowly seeps into surface waters,
including rivers, streams, and bays.
Watersheds are complex systems that can be altered by natural
occurrences and/or human activities. In fact, most of what happens to a
stream occurs outside its immediate channel but within the watershed.
Because of their sensitive balance, streams are indicators of events that
occur on the land in the watershed. Activities in a watershed have the
potential to affect not only the nearest stream but the downstream water
bodies as well.
This means that litter, chemicals, fertilizers, and other potentially
harmful substances all find their way into the water. On paved areas
this matter runs even faster towards streams and rivers because
there is no soil or roots to soak up the liquid and filter out the
pollutants. Contaminants such as fertilizers, pesticides, and
hazardous chemicals leaching from yards, farms, factories, and
landfills can seep into groundwater and, eventually, into the surface
water of a watershed.
In a watershed, everything is connected. For example, pollutants may seem minor
and insignificant in a tiny stream, but they add up in a river, and even more so in
a bay. Sediment is another example. A little sediment is relatively harmless in the
upper reaches of a stream. However, further down that stream where other
streams join it, the sediment adds up and the water begins to get cloudy; this
cloudiness kills the grasses that provide habitat for fish and food for waterfowl.
Eventually all streams and ditches, and everything they carry, empty into the
Chesapeake Bay. Because the Bay does not flush into the Atlantic Ocean there's
nowhere for these pollutants and sediments to go. Contrary to popular belief, the
Bay cannot dilute large quantities of chemicals because it is very shallow; therefore
everything that goes into the Bay, stays in the Bay.
