Fewer water samples tested from the Chesapeake Bay this summer had dangerously low levels of oxygen compared to previous testing, according to data released by the state Thursday.
Scientists found, on average, that 13.6 percent of the bay’s waters tested this summer did not have enough dissolved oxygen to support a healthy ecosystem, known as “dead zone” waters, the Department of Natural Resources reported.
That compares to the average of 18.9 percent since 1985. The best year on record was 2012, when 13.3 percent of the bay lacked sufficient oxygen.
Dissolved oxygen is vital for aquatic life such as fish, crabs and oysters. The “dead zone” is defined as water that has dissolved oxygen concentration of less than 2 milligrams per liter of water.
The Chesapeake Bay Foundation, a nonprofit advocacy group, said the report shows that efforts to improve the bay’s health are paying off.
“There is scientific consensus that the dead zone is getting smaller over time, and ending earlier in the summer,” said Beth McGee, the foundation’s director of science and agricultural policy. “This is an indication that the Clean Water Blueprint is working. But we also know that much more needs to be done to achieve a bay that is healthy for all living creatures.”
Maryland’s scientists could not offer an estimate of the overall volume of this summer’s dead zone, because some of their water quality sampling was incomplete due to rough and windy conditions.
At the beginning of the summer, scientists predicted the dead zone would be about 1.89 cubic miles in size — nearly the volume of 3.2 million Olympic-sized swimming pools.