Some fish and crabs may be able to swim away from areas without enough oxygen. But other animals – such as oysters, clams and worms – are not able to swim away, and can die if there is not enough oxygen around them.

Scientists usually use an electronic dissolved oxygen meter to measure the amount of oxygen in the water.

Like all other species in the Chesapeake Bay, blue crabs need oxygen to survive. In rare cases, blue crabs have been known to come out of the water onto land to escape oxygen-deprived waters. This phenomenon is known as a “crab jubilee.”

Oxygen gets into the water when:

• Oxygen from the atmosphere dissolves and mixes into the water’s surface
• Algae and bay grasses release oxygen during photosynthesis
• Water flows into the Bay from streams, rivers and the ocean. Ocean waters generally have more oxygen. River waters are fast-moving, which helps oxygen from the air mix in.

Sometimes the Bay’s deeper waters have little or no oxygen while surface waters have more oxygen. This usually happens in summer because of a combination of factors, including temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom.

Scientists generally agree that the Bay’s creatures need dissolved oxygen concentrations of 5.0 mg/L or more to live and thrive. However, the amount of oxygen an animal needs varies depending on how large or complex the animal is and where it lives.

Temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom all interact with each other to affect the amount of oxygen in the water.

Just like humans, all of the Chesapeake Bay's living creatures – from the fish and crabs that swim through its waters to the worms that bury themselves in its muddy bottom – need oxygen to survive.