Good water contains enough dissolved oxygen and is sufficiently clear to support the tremendous variety of aquatic life found in the Bay. In many areas of the Chesapeake, and for much of the year, the quality of the water is not sufficient to support the Bay's living resources. In the warmer months, large portions of Chesapeake Bay contain little or no dissolved oxygen. Low oxygen conditions may cause the eggs and larvae of fish to die. The growth and reproduction of oysters, clams and other bottom-dwelling animals are impaired.
Adult fish find their habitat reduced and their feeding inhibited.
Many areas of the Bay also have cloudy water from an overgrowth of algae or too much sediment in the water. Without SAV, critical habitat for fish and crabs is lost. Although there has been a resurgence of SAV in some areas of the Bay, most areas still do not support abundant populations as they once did. The main causes of the Bay's poor water quality and aquatic habitat loss are elevated levels of two nutrients, nitrogen and phosphorus. Both are natural fertilizers found in animal wastes, soil, and even the atmosphere.