The ghosts are all around the gently rolling farmlands of eastern England. But you have to know where to look.

These are not the kind of phantoms that scare or haunt – they are ghost ponds. Over the years, landowners buried them, filling in wetlands so they had more land for planting crops and other needs, or let their ponds fade away with neglect. Along with those ponds, they erased entire ecosystems – and contributed to the decline of wetlands worldwide.

The result: an array of environmental calamities, ranging from rising floods to species hurdling toward extinction.

There are some who are trying to reclaim these lost waterbodies. In eastern England, a motley team of farmers, university researchers, and conservationists is digging into the region's barley and wheat fields to turn back the clock.

With chain saws, an excavator, and plenty of sweat, it takes just a few hours to resurrect one dying pond near Hindolveston, a thousand-year-old village not far from the North Sea. They fell trees and shrubs, then start digging until reaching their goal: an ancient pond bottom that once supported insects, aquatic plants, and the birds and animals that feed on them.

"As soon as they get water and light, they just spring to life," says Nick Anema, a farmer in nearby Dereham who has restored seven ponds on his property. "You've got frogs and toads and newts, all the insects like mayflies, dragonflies, damselflies. ... You can't really beat a pond."

But the battle for the wetlands is a struggle. While efforts are under way to stem losses and regain some of what's been lost, wetlands around the world continue to be filled in and plowed over.

Almost 90% of the world's wetlands disappeared over the past three centuries, according to the Ramsar Convention, an organization formed around a 1971 treaty to protect wetlands. And the losses have accelerated since the 1970s.

The consequences are profound – wetland-dependent species threatened with extinction, more severe flooding, and the release of huge amounts of the greenhouse gas carbon dioxide.

Climate change threatens to worsen the problem. Warmer temperatures and changing rainfall patterns can trigger drought, leading to more pumping of water reserves that would otherwise feed surface wetlands, scientists say.

"We now know the value of wetlands, and we know with increasing precision how many wetlands we're losing. The next step is for the governments to act," says Royal Gardner, director of the Institute for Biodiversity Law and Policy at Stetson University in Florida.

A few hours of heavy rain in North Dakota are all it takes to transform the dry, cracked earth of the prairie into thousands upon thousands of pocket-sized wetlands.

The rain pools in shallow depressions known as prairie potholes and quickly flushes out insects from beneath the soil.

Each pothole becomes a haven for a pair of ducks. Two blue-winged teals dabble on one pothole. On the next pothole are two more ducks, then two more and so on to the horizon.

But to farmers, these wetlands carved into the earth by glaciers some 10,000 years ago can be an adversary. They bog down tractors and can kill young crops, leaving patches of lifeless stalks.

Some farmers steer around them, planting in swirling patterns to avoid wet areas. Other times, the wetlands are removed, often to make way for corn.

Despite their mind-boggling numbers – several million potholes are spread across a region that covers portions of five states and three Canadian provinces – these wetlands are steadily blinking out. One by one, they're being drained or plowed under.

Only human-made wetlands buck the trend toward global decline. Rice paddies, reservoirs, and agricultural stock ponds all increased in acreage since the 1970s, according to Ramsar.

Barton Schott, a third-generation farmer in the small community of Kulm, North Dakota, recently installed networks of perforated pipes beneath some of his fields to drain off the standing water. He must offset the losses under federal regulations, installing a berm across a low area in different field to create a small pond.

The guiding principle is to have "no net loss" of U.S. wetlands. A similar tactic has been adopted in China.

Yet in both nations, scientists are concerned that the approach papers over significant differences between natural wetlands and those created by humans. That's because constructing ponds or reservoirs with water year-round doesn't fulfill the same ecological role as the smaller wetlands they replace.

"People brag about the fact that there's been no net loss. But what they've done is destroy natural wetlands and created artificial ones," says Stuart Pimm, a Duke University professor.

Since the start of the 20th century, 75% of the United Kingdom's ponds have been lost.

Nick Anema describes how his view of farming differs markedly from his father's, who regarded the natural world as an obstacle to overcome. For Nick Anema, farming and preservation are inextricably linked.

In 2013, he saw an advertisement seeking farmers who would be willing to have ghost ponds on their property excavated as part of a research project.

He suspected a low point in one of this fields fit the description of a ghost pond and a check of old maps confirmed it. By the time the excavation wrapped up, water already was pooling at the bottom.

After ghost ponds are dug out, seeds from long-buried water plants come to life, including in one case a pond on Mr. Anema's farm that had been filled in an estimated 150 years ago. And as the plants come back, so do the insects that depend on them, followed by fish and birds that eat the insects.

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"They've done just what we hoped," says Carl Sayer, a researcher at University College London. "They're wonderful, healthy, vibrant ponds,"

This story was reported by The Associated Press. Matthew Brown reported from North Dakota.