(Barbara Haddock Taylor/Baltimore Sun)

Maryland environmental scientists gave the Chesapeake Bay a “C” for overall health in 2016, with improved fish populations and water conditions contributing to the second-highest grade the ecosystem has received in 30 years of scoring.

The report card released Monday by the University of Maryland Center for Environmental Science showed that the bay is 54 percent of the way toward achieving key health benchmarks, an uptick of one percentage point compared with the previous year.

Experts cited the results as proof that efforts to clean up the estuary are working.

“While only a slight improvement, it’s encouraging that the overall health remained steady despite many pressures on the Chesapeake Bay and across its watershed,” said Bill Dennison, a top scientist with the center.

Sen. Benjamin L. Cardin (D-Md.), speaking at a news conference in Baltimore, called for continued federal support for bay restoration. He noted that President Trump this year proposed slashing funding for Chesapeake Bay cleanup efforts. Congress last month approved a fiscal 2017 budget that maintains funding for the bay at $73 million, the same level as the previous year.

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“The long-term investment is working,” Cardin said. “We can’t slow down. . . . It’s critically important to maintain the strong federal role.”

The bay’s highest score on record, 55 percent, occurred in 2002. The Chesapeake earned its lowest score, 36 percent, the following year. The Center for Environmental Science awards an “A” for scores of 80 to 100 percent; “B” for 60 to 79 percent; “C” for 40 to 59 percent; “D” for 20 to 39 percent; and “F” for anything lower than that.

In 2016, Chesapeake Bay fisheries received an “A” for health of the blue crab, anchovy and rockfish populations. Blue crabs scored 90 percent, improving drastically compared with two years ago, when the grade was 32 percent.

The total area of the bay covered by aquatic grasses, which provide habitats for blue crabs and rockfish, had increased in most regions, but a few tributaries showed declines, including the Patapsco and Back rivers near Baltimore.

Those two rivers received a failing grade for overall health but improved their scores to 27 percent, an increase of six percentage points compared with 2015.

The report said the Chesapeake is meeting its long-term goals for reducing levels of phosphorous and nitrogen, which fertilize algae blooms that choke off sunlight needed for aquatic grasses and create “dead zones,” where oxygen is scarce.

The phosphorous score reached 82 percent, an improvement of 12 percentage points over the past year and the highest score since tracking of the data began in 1986. The nitrogen score fell three percentage points, to 55 percent, but remained in the “moderate” range.

Dennison attributed the bay’s passing health grade to programs at every level of government aimed at cleaning up the estuary, including sewage-treatment upgrades, efforts to limit storm-
water runoff, increased planting of winter crops to absorb excess fertilizer from farms, and the federal Clean Air Act, which he credited with reducing the amount of nitrogen in rain and snow.

He said a program that Maryland started last year to limit the amount of manure that farmers use to fertilize their fields will help continue the improvements.

The grades came as the Maryland Environment Department announced it had approved portions of the Choptank River in Dorchester and Talbot counties for shellfish harvesting, although harvesting of oysters will still be prohibited in those areas.

Agency officials said the reclassification of those areas was because of decreased bacteria levels.