For a second-straight year, the Chesapeake Bay posted a passing C grade in an evaluation by state environmental scientists — a sign the bay's health is holding steady, according to scientists.
The report card issued by the University of Maryland Center for Environmental Science showed a modest gain in the bay's marks — one percentage point higher than a year ago — but the rating is nonetheless among the highest out of three decades of data. It indicates the estuary is 53 percent of its way toward reaching certain ecosystem health benchmarks.
A measure of blue crab, rockfish and anchovy populations showed its highest score in a decade, and waters around Baltimore posted the strongest improvements of any region of the bay last year — though they still received poor grades.
"While this is only a slight improvement, it is encouraging to see health remaining steady despite many pressures on the Chesapeake Bay and its watershed," scientists wrote in the report.
State officials credited years of regional efforts to reduce pollution from runoff for the improvements. They stressed that federal oversight of state programs, which the administration of President Donald Trump has proposed to dismantle, has been and remains vital to maintain progress.
"The long-term investment is working," Sen. Ben Cardin said at a Monday news conference at the center's Institute of Marine and Environmental Technology in Baltimore. "We're on that path. We can't slow down."
The most promising indicators of bay health last year were relatively high levels of dissolved oxygen in the water, as well as declining levels of phosphorus. Both those elements are meeting long-term goals.
Another indicator, nitrogen levels in bay waters, declined only slightly in 2016, but scientists said they have nonetheless fallen significantly in the long term. Nitrogen and phosphorus fertilize algae blooms that block sunlight from reaching underwater grasses and create "dead zones" with little or no oxygen when they decompose.
Water clarity and aquatic grass abundance remain relatively poor, the report found, but scientists said the improvement seen in both indicators shows renewed resilience in the ecosystem.
"I really believe we're at a tipping point," said Nicholas DiPasquale, director of the Environmental Protection Agency's Chesapeake Bay Program office in Annapolis.
The Trump administration proposed eliminating that $73 million program, which coordinates state-level bay cleanup efforts, but federal lawmakers preserved it for a year in a budget deal reached last week.
Around the bay, indicators showed the strongest improvement in the Patapsco and Back rivers around Baltimore and Baltimore County. Still, the rivers were graded a D, the lowest of any bay region. The waterways of Anne Arundel County received a D+, while Harford County rivers got a C- grade.
The highest score on the report card, a B, went to the Virginia portion of the bay's main stem.
"In the past, we've had Fs," said Bill Dennison, vice president for science application at the environmental science center. "We've never had an A yet."
The report card results are on par with high scores from 2002 and 1992, both years when drought reduced the amount of nutrients and other pollutants that flowed into bay waterways.
Given largely normal precipitation across the bay watershed in 2015 and 2016, bay advocates attribute the recent score improvements to new bay-friendly policies, such as requirements that governments and developers build gardens around paved surfaces and incentives that encourage farmers to plant cover crops.
Scientists acknowledged that a major tropical storm, hurricane or other heavy rainfall event could set back the progress shown in the report card. But they said the ecological improvements make the bay more capable of bouncing back.
At the same time, they said climate change will pose new challenges to the bay's recovery.
The environmental science institution has released the report card every year since 2006. Using the same criteria, they also have graded bay conditions going back to 1986.
The report card follows promising results from other surveys of bay health state officials released last month. The number of female crabs in the bay, a key indicator of the species' resilience, is at its highest since at least 1990. Underwater grasses are also at their most abundant in decades.
"Once you reach a point where you've overcome the inertia of the system," DiPasquale said, "these indicators start building on each other."