BALTIMORE (WJZ) — A report card of C may be average but it’s reason for optimism when it comes to the health of the Chesapeake Bay.

Alex DeMetrick reports “C” is the best grade researchers have given the bay since they started an annual report card.

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The Chesapeake Bay is only as healthy as the water that flows into it from six states. For example, in Maryland, the Potomac River is now carrying less sediment and nutrient pollution, like nitrogen. But the Patapsco and Jones Falls are still heavy polluters.

But when all sources are balanced out…

“This is the first report card we can report significant, positive improvements,” said Dr. William Dennison, University of Maryland Center for Environmental Science.

Like clearer water and more bay grasses.

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For 10 years, the University of Maryland’s Center for Environmental Science has been grading the bay’s health. The current report card gives the upper bay a C, the same grade for the middle bay and a B for the lower bay, for an overall grade of C. It used to be Ds and Fs.

“We know what we’re doing is working; we just need to finish the job,” said Dr. Donald Boesch, University of Maryland Center for Environmental Science.

What’s working is improved sewage treatment and power plants releasing less nitrogen and more farms that plant cover crops after the fall harvest to absorb leftover fertilizer. What’s still to be done is control the chemicals that wash off hard surfaces.

“The runoff from stormwater. If we can nail that, we’ll turn this bay around,” said Dennison.

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Those hard surfaces increase constantly, as 150,000 new residents move into the bay’s watershed every year.