The Chesapeake Bay’s ecological health improved slightly last year, according to a new assessment, with three of the estuary’s key fish populations in their best shape in decades.

For the fifth straight year, the Bay’s condition in 2016 earned a C grade on the annual report card produced by the University of Maryland Center for Environmental Science. The overall score — combining measures of water quality, habitat and fish abundance — ticked upward to 54 percent, a 1 percent gain over 2015.

Sen. Ben Cardin, D-MD, and officials from Maryland and the Environmental Protection Agency turned out for a press conference in Baltimore's Inner Harbor to celebrate the Bay's progress, while cautioning that much more needs to be done.

"It gives us all who didn't start out getting good grades hope," Cardin said.

While not a huge improvement, the score is the second highest the Bay has earned since the annual assessments began in 1986, with only 2002 rating slightly higher. The scientist overseeing the report card said he takes heart from that, and the fact that the Bay’s health has held steady in recent years despite many pressures on it, both natural and man-made.

“I’m more optimistic than I’ve been in a long time,” said Bill Dennison, vice president for science applications at UMCES. “This seems to be sustained.”

The improvement seen by the UM scientists agrees with a report card issued earlier this year by the Chesapeake Bay Foundation. The Annapolis-based environmental group upgraded its assessment of the estuary’s health from a D to a C-minus. And, the annual Bay Barometer released by the state-federal Bay Program partnership also found many key indicators ticking upward, though it did not give an overall grade.

Bay health has tended to vary with the weather, and water quality, in particular, fares better in drought years. Less precipitation washes less nitrogen and phosphorus off the land that feed algae blooms and lowers the dissolved oxygen in the water that fish need to breathe.

But Dennison said he’s seeing evidence that the Bay’s water quality is holding its own, even in years when precipitation approaches normal. He suggested that’s likely the result of Baywide efforts to reduce nutrient and sediment pollution.

“It’s not just a blip from a drought year and then it comes crashing down,” he said. “We’ve had average runoff the last few years, and it’s steadily gotten better.”

Bay grass abundance has improved, and the oxygen-starved “dead zone” that forms every summer in the deepest part of the estuary has shrunk in recent years, Dennison noted.

The UMCES assessment rated fisheries health at 90 percent last year, up from 73 percent in 2015 and the highest score ever. That grade represents an average assessment of abundance for three key species — striped bass, blue crabs and Bay anchovies.

Other important species, such as oysters and American shad, remain in doubt, Dennison acknowledged. But he said that the three species rated by UMCES are important indicators of overall fish health in the Bay. Two are pillars of the commercial fishing industry, while the third, tiny anchovies, serve as food for all of  the larger species in the estuary.

Mark Belton, Maryland's natural resources secretary, welcomed the finding of improved fish abundance at the press conference, saying that "regardless of partisan politics and sniping" the Hogan administration is committed to restoring and sustaining the Bay's fisheries. The administration has been criticized by environmentalists and Democratic lawmakers for firing a veteran crab fishery manager and for moving to open oyster sanctuaries in response to complaints from some watermen.

Water quality earned mixed scores in the report card. Dissolved oxygen and phosphorus improved, while nitrogen pollution worsened, and the abundance of bottom-dwelling worms and other marine life declined some.

And while the “dead zone” in the Bay may have shrunk, dissolved oxygen levels in its tidal tributaries remains a concern.

“We still have big problems in (places such as) the upper Choptank, the upper Chester,” Dennison said. “In that shallow water at night, it (dissolved oxygen) just plummets.”

Another problem has cleared up some, literally, though no one knows exactly why. Water clarity, which had been in a long-term decline, has improved noticeably in the last couple years. Clearer water has been most pronounced in the central region of the Bay, Dennison said, including tributaries such as the Choptank and Severn rivers.

“I’ve been poking around the Choptank since 1987, and I’ve never seen it like that,” he noted.

“We still don’t understand why,” he added, calling it an “enigma” that scientists are still trying to unravel.

Dennison also said he was heartened by the improvements seen in some of the Chesapeake’s most distressed tributaries. The Patapsco and Back rivers by Baltimore, which got an F grade as recently as 2014, saw the biggest gain, earning a D grade for 2016.

The Elizabeth River in Norfolk had also been among the Bay’s sickest rivers, but conditions there rated a D last year as well. Rivers on the Lower Western Shore of Maryland earned a D-plus for 2016, but are showing signs of improvement, according to the report cards. Of the other rivers that have long been in poor condition, only the Patuxent in Maryland and York in Virginia showed no gains last year.

But Dennison said that from what he’s seen, he is confident that if the Bay cleanup continues on its present course, even the Chesapeake’s least healthy tributaries will get better.

“We’re going to get out of the Ds," he predicted. But with only a C grade so far, the Bay still has a long way to go to be considered fully restored, he said, and climate change is not going to make it any easier to get there.

At the press conference, Cardin and UM officials warned that further progress in the Bay depends on continued federal involvement. The Trump administration has proposed eliminating federal funding for the federal-state Bay Program, which received $73 million this year, and cutting other federal programs that also aid the restoration effort. Two-thirds of those funds go to the states, noted Nicholas DiPasquale, director of EPA's Bay Program office, some of it to underwrite pollution reduction projects but some also for monitoring and modeling the efficacy of what's been done and is planned.

"Without federal investment, it's going to be hard to gather the fact and figures to tell how we're doing," said Donald Boesch, president of the UM environmental science center.

For now, though, Dennison said it's good to celebrate the progress that's been made. Not that long ago, he recalled at the press conference, the Bay was in the ecological equivalent of the emergency room, with declining water quality and habitat. Now, he concluded, "We've moved that patient from critical condition over to the ICU."

For details of this and earlier report cards, go here.