Chesapeake Bay is wide and shallow, so contains a small amount of water for an estuary of its size. It also has a very large area of watershed for its volume of water, and thus is quite susceptible to contamination from activities in the watershed. Originally almost entirely forested, the watershed now is the site of coal mining, industry, agriculture and, increasingly, urbanization. A forest acts like a sponge, evening flows and filtering nutrients. Without its forests, the watershed is prone do delivering bursts of freshwater, contaminated with nutrients and worse into the Bay. To save the bay, it is necessary to reclaim at least part of the forests function in the watershed.