The Chesapeake Bay restoration plan is fueling the most robust resurgence of underwater grasses and submerged aquatic vegetation in the world, according to a new study.

The study credited the growth to a federal and multistate effort to restore the bay’s health, a project that President Trump plans to eliminate. The plan has reduced nutrient pollution, which comes from human-managed waste and runoff from farms and cities that flow into the nation’s largest estuary. The region’s population has more than doubled to 18 million since 1950, and runoff triggered a crisis by dramatically lowering the levels of oxygen and sunlight that vegetation needs to survive.

Scientists say submerged vegetation is the bay’s “secret garden” because it serves as a protective nursery for numerous species of marine life and waterfowl.

Threatened by the loss of animals that support commercial and recreational fishing, along with tourism, the six states in the bay watershed embarked on a cleanup plan in 1984. After that faltered, the largest federally managed cleanup of a water body in the nation’s history followed  in 2010.

The combination of cleanups over the three decades analyzed in the study reduced pollution from rural farms and urban water treatment facilities by 23 percent. Over that span, submerged aquatic vegetation in the bay has increased by 316 percent.

“Other regions have seen large resurgences in sea grass cover with improved water clarity, such as Tampa Bay, Fla., or improved sediment stability, as in the Wadden Sea [in Northern Europe], but the Chesapeake Bay has seen greater total and proportional recovery than any other submerged aquatic vegetation restoration project of which we are aware,” according to the study, which was published Monday in the Proceedings of the National Academy of Sciences.

The cleanup not only helped submerged vegetation but increased its biodiversity, said Jonathan Lefcheck, a researcher for the Center for Ocean Health at the Bigelow Laboratory for Ocean Sciences in Maine, who was the lead author. That’s important because some species are better than others at surviving catastrophic events such as tropical storms that can devastate vegetation and grass beds.

Susquehanna Flats, an area of the bay near the Susquehanna River, was found to have up to 14 species.

“If you get a bunch of species together, there may be a few species in that diverse community that can withstand that disturbance so it doesn’t wipe out everything,” Lefcheck said. “They make it hospitable for other species to come back and colonize. We can say beds that have more species are more deserving of our attention.”

Anyone who scuba dives to the vegetation and quietly lies there will immediately realize its importance, said Bill Dennison, a researcher at the University of Maryland Center for Environmental Science, who was an author of the study. “If you let them come to you, you see sea horses and clams and scallops and inchworms and snails crawling up and down the blades. I’ve come out of the water with thousands of these snails. It’s teeming with life.”

Among those animals are blue crabs.

“Most of us don’t appreciate the life cycle of the blue crab, how it comes from the bay to the plate,” said Robert Orth, a researcher at the Virginia Institute of Marine Science at the College of William & Mary. “These little babies in the first 30 days of their life stay on the coast of Virginia near North Carolina.” Then they make a run into the bay and its tributaries toward shallow areas and grass beds. “It’s their home…. They support an incredible array of other animals that act as food for the blue crabs. The grasses grow by themselves. They don’t need fertilizer.”

But the expansion of vegetation could be short-lived. Trump’s 2018 budget seeks to eliminate the Chesapeake Bay Program’s $73 million annual funding. Congress is more supportive of the program: The House approved a $13 million cut, and the Senate voted to restore the program’s full budget. The proposals are wrapped up in an omnibus bill that is being negotiated under a March 20 deadline, according to the Chesapeake Bay Foundation.

Farmers, developers and the chemical industry oppose some of the restrictions on pollution from development sites and farms, including fertilizer and animal manure that pours into creeks, rivers and other tributaries.

That nutrient pollution fuels enormous algae blooms that suck away oxygen. Algae also builds on blades of grass and leaves, then floats to the surface as scum that blocks light. Without light, plants die. Submerged vegetation requires more light to survive.

The American Farm Bureau Federation, joined by farmers in Pennsylvania and the National Association of Home Builders, lost a federal suit to stop the program. They appealed to the Supreme Court, which declined to hear the case two years ago. Trump could reverse their loss.

Dennison, a study author, said a group of environmental scientists in the bay region decided to undertake the study two years ago. Other researchers are based at Virginia Institute of Marine Science at the College of William & Mary, the Smithsonian Environmental Research Center, St. Mary’s College and the Maryland Department of Natural Resources and the Center for Ocean Health.

Dennison was also part of a group that conducted a global analysis of sea grasses 10 years ago. “We called attention to a global decline that’s occurring around the world,” he said. “We called those coastal canaries [in a coal mine]. These high light requirements are what makes them the canary. When the canary goes, you still have a little time. You get yourself and that canary out of that mine. You act decisively. Just as they’re the first thing to go, they’re also going to be the harbinger that something’s wrong.”

Although the news is positive, “we are not saying mission accomplished,” said Dennison.

Jennifer Keisman, a scientist at the U.S. Geological Survey in Baltimore, said “there is still much work left to be done. It’s estimated that only 40 percent of the Bay met water quality standards in 2016.” She said one example is the Chesapeake’s dead zone, a large expanse of oxygen-depleted water in which nothing can survive. “We’re only 40 percent toward the cleanup plan’s goal of reducing hypoxia,” or oxygen depletion, in parts of the Chesapeake, she said.

The Eastern Shore where the Choptank and Wicomico rivers are surrounded by chicken farms is lagging behind the rest of the bay.

“This is not the time to stop,” Orth said. “The chicken farms are going nuts. Everywhere you go is chicken, chicken, chicken. Everyone likes their wings.”

Correction: An earlier version of this post misattributed the final quote to Jennifer Keisman.