Dead zones are created by hypoxia and the bacterial decay of dead phytoplankton.
The Chesapeake Bay, like many other bodies of water, is overrun with nutrients, which results in a type of pollution called eutrophication. Every spring, sewage treatment facilities, farms, and lawns release large amounts of nitrogen and phosphorus into the Bay. These nutrients fuel the growth of algae as the water warms up in the summer, resulting in blooms that deplete the water's oxygen content and create sizable "dead zones" where fish, crabs, and other aquatic life find it challenging to survive. During these times, some of the mud's surface layers and portions closer to the bottom may become anoxic, meaning there is no oxygen present at all.
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