Several key health indexes relating to the health of the Chesapeake Bay improved slightly from the previous year, officials said at a news conference Tuesday.

The University of Maryland Center for Environmental Science gave the overall health of the bay in 2020 a C grade, slightly up from the previous year’s C-minus. The watershed, which includes off-shooting rivers and basins, was rated a B-minus. According to the UMCES annual report, the bay showed moderate health and the watershed showed good health last year.

“The result of the report card are clear: We’re making some progress,” Maryland environmental secretary Ben Grumbles said. “But we have our work cut out for us.”

Seven of the 15 reporting areas in the bay saw improvements, with the highest-scoring region in the lower bay and the lowest-scoring region by Maryland’s Patapsco and Back rivers.

Key changes included a decrease in nitrogen levels, which earned a report-card grade of 64 percent — up from last year’s 39 percent. The decline was attributed to the decrease in pollution and travel during the coronavirus pandemic.

However, scientists warned that the long-term impact of the pandemic on the ecosystem’s health remains largely unknown, and said the pandemic prevented scientists from monitoring the bay between March and May of last year.

The scores for the amount of dissolved oxygen also improved in 2020, while other metrics like water clarity and aquatic grasses fell slightly.

William Dennison, the vice president of science applications at UMCES, said the scores for aquatic grasses may be misleading because high-salinity eelgrass was drastically harmed by two consecutive high-temperature summers, but have been offset by a large expansion of thriving freshwater grasses.

Water quality also declined, but scientists have yet to understand the reasons behind the fluctuating quality, Dennison said.

Chlorophyll scores fell, too. While nutrients levels are generally declining, which prevents harmful oxygen-depleting algae blooms in the bay, chlorophyll levels rose last year because of the timing of the nutrients entering the bay, he explained.

Officials said the data from the Chesapeake Bay watershed was most promising. The West Branch Susquehanna received an A-minus rating in overall health, 15 other regions were rated in good health and seven were rated in moderate health, according to the report.

UMCES has collected data on the bay for the last 34 years, and this year they added new socioeconomic metrics to measure the health of the watershed. The amount of protected land was among these new indexes and received a B rating.

The Chesapeake Bay Program’s 2014 Watershed Agreement aims to preserve 2 million acres by 2025. According to data collected through early 2019, nearly 1.36 million acres of land in the watershed had been permanently protected since 2010.

A different biannual report from the Chesapeake Bay Foundation, which was released earlier this year, showed a slight decline in the bay’s overall health. That rating was 32 — down one point from 2018 because of ineffective management of the bay’s striped bass population, which is unrelated to the water, according to the report. It maintained a D-plus rating for the bay, similar to the 2018 report.

Prior years had shown steady growth in the CBF report — largely due to a 15-year, $19 billion cleanup plan administered by the Environmental Protection Agency, which holds the six states in the watershed to specific pollution limits.

In 2018, scientists considered the bay to be in its best shape in the last 33 years, according to the CBF report. A year later, health indexes dipped for the first time in a decade, which Chesapeake Bay Foundation president William Baker attributed to efforts from then-President Donald Trump to roll back environmental progress and slash Chesapeake Bay restoration funding.

Data from the CBF report released in January also revealed a long-term trend of a shrinking “dead zone,” or oxygen-depleted waters that are uninhabitable for fish, oysters and other creatures.

Peter Goodwin, president of UMCES, said scientists realized that states in the watershed would have to take on larger commitments due to climate change projections.

“For each state there’s very detailed milestones to meet, and should we not meet those milestones, there’s the chance to make additional adjustments to make sure the progress is being made,” Goodwin said.

Still he said the scientists are hopeful for the future of the bay — the nation’s largest estuary — citing the incremental improvements they have seen in the past few years and the large investments being made to protect the area.