Overall, however, the proportions of fresh and salt water in the Bay depend largely on the amount of rainfall that flows out of the Chesapeake's major rivers. Salinity is one of the most important physical features in determining what lives in a particular part of the Bay, so plant and animal populations in the Bay differ north to south, west to east, and from year to year. Temperature and bottom sediment also determine the distribution and abundance of organisms. Estuaries teem with a variety of plant and animal life. The constant movement of the tides sweep away wastes and circulates nutrients and food, providing a favorable situation for sedentary animals such as oysters and clams.
Estuaries are important nursery grounds for fish.
Indeed, many kinds of aquatic animals spend some portion of their life cycles in estuaries. The enormous biological productivity of estuaries is reflected in their immense commercial importance. The Watershed A thorough examination of Chesapeake Bay ecology includes not only the body of water itself, but also the entire drainage area, referred to as the Bay watershed . The Chesapeake Bay watershed includes all the land from which water drains right into the Bay or into one of its tributaries. Water which falls onto land outside the Chesapeake Bay watershed will drain into some other body of water - Delaware Bay, the Ohio River, the Atlantic Ocean, or any number of streams or lakes.