The Chesapeake Bay suffers from "dead zones," which are caused by inadequate oxygen in the bay's waters.
There was less oxygen in the depths of the Chesapeake Bay last year. The Chesapeake Bay Program says oxygen levels in the bay dropped by about 4 percent in 2011. Compared to a decade ago, the Bay in 2011 had less than half as much oxygen dissolved in its water.
Things living in the bay need oxygen to breathe, and millions of of creatures die each year from suffocation when dead zones develop every summer. The culprit is nitrogen and phosphorous pollution that washes in from cities and fields and waste water treatment plants up stream.
Algae feed on that, grow into giant blooms, and then suffocate everything else in the middle of the bay. Heavy rains last year washed extra pollution into the body of water.