By the Numbers: 3 milligrams per liter

Like animals on land, critters in the Chesapeake Bay need oxygen to survive. But persistent nutrient pollution—and the algae blooms that result—mean some fish and shellfish have a hard time finding the oxygen they need to survive and thrive.

Under water, oxygen is present in dissolved form. When nutrient-fueled algae blooms die, the bacteria that arrive to decompose them use up oxygen in the water, leaving little for fish and shellfish and creating so-called “dead zones.” Increased nutrient pollution leads to larger algae blooms, which in turn create more dead zones.

Scientists measure dissolved oxygen as part of their work to determine the health of an ecosystem. Because an animal’s size and habitat determine how much oxygen it needs, scientists have set different dissolved oxygen standards for different aquatic habitats at different times of the year. An American shad, white perch or other fish found in shallow water, for instance, needs more oxygen than a worm, clam, oyster or other invertebrate found on the Bay’s bottom. While the former thrive at dissolved oxygen concentrations of 5 milligrams per liter of water, the latter need just one. The Bay’s infamous blue crabs and oysters, on the other hand, need dissolved oxygen concentrations of three milligrams per liter to thrive.

According to recent data, between 2011 and 2013, 24 percent of the water quality standards for dissolved oxygen were met in the deep-water habitat where bottom-feeding fish, blue crabs and oysters are found. Because the Chesapeake Bay Program has set a goal to achieve the clean water necessary to support aquatic resources and protect human health, our partners are working to reduce pollution and bring the Bay up to water quality standards. Learn how you can help.