Chesapeake Bay is the largest estuary in the US. Its main course, fed by the Susquehanna River, is over 185 miles (300 km) in length. It has numerous sub-estuaries, and more than 150 rivers and streams drain into it. This body of water was created by sea-level rise drowning the valley of the Susquehanna and its tributaries over the last 15,000 years. Once famous for its seafood, such as oysters, clams, and crabs, the bay is now far less productive, though it still yields more fish and shellfish than any other estuary in the US. Industrial and farm waste running into the bay causes frequent algal blooms, which block sunlight from parts of its bed. The resulting loss of vegetation has lowered oxygen levels in some areas, severely affecting animal life. The depletion of oysters, which naturally filter water, has had a particularly harmful effect on the bay’s water quality.
In the 1990s, drilling of the seabed at Chesapeake Bay led to the discovery of a meteorite impact crater 53 miles (85 km) wide under its southern region. The 35-million-year-old crater helped shape today’s estuary.