The levels of dissolved oxygen within the Chesapeake Bay plummeted in July after a promising start to the summer.
The Baltimore Sun reports that state environmental officials are blaming a recent heat wave for the decline since warm water holds less oxygen than cold water.
The Department of Natural Resources wrote in a statement that a lack of winds also prevented surface oxygen from mixing with bottom waters to increase the oxygen levels.
In late July, 1.65 cubic miles of water along the bottom of the bay contained little or no oxygen, more than an average of 1.29 cubic miles for late July.
Dissolved oxygen levels are vital for creatures such as blue crabs, striped bass and anchovies.