MONROE, Mich. — Honking geese soar overhead in a V formation, buffeted by bitter gusts off nearby Lake Erie, while flocks of mallards bob along the shore. Even blanketed in snow, the sprawling wetland in southeastern Michigan is a magnet for water birds — one reason a public-private project is underway to improve it.

Crews are building levees, canals and pumps that will regulate water levels and upgrade fish passageways in a 946-acre section of Erie Marsh, making it a better home for wildlife and limiting the spread of invasive plants.

It’s an example of decades-old efforts by government agencies and private groups to rebuild Great Lakes coastal wetlands such as swamps, bogs and marshes that have been depleted by development. A federal report released in November suggests the work is beginning to pay off.

The eight-state Great Lakes region — extending from western New York to eastern Minnesota— was the only section of the U.S. where coastal wetland acreage increased during a five-year period when scientists took extensive measurements with satellites and field photography.

The gain was modest — 13,610 acres, an area not quite as large as the New York City borough of Manhattan. Yet it happened as the rest of the nation’s coastal wetlands shrank by 360,720 acres. The loss amounted to less than 1 percent of the U.S. total, but continued a longtime negative trend.

Wetlands don’t have the cachet of spectacular natural features that oceans and mountains do. They’re sometimes dismissed as worthless, especially by those wanting to cover them with shopping centers or highways. But they are immensely valuable, helping prevent floods by absorbing excessive rainwater. They are known as “nature’s kidneys,” filtering out pollutants that otherwise would wash into lakes and rivers, and also provide vital wildlife habitat — nesting grounds for ducks and geese, temporary refuges for migratory birds, spawning areas for fish.

Scientists said the continental U.S. has lost roughly half the wetland acreage that existed prior to the European settlement era. They’ve been relentlessly filled and drained for farms, housing and cities.

The biggest losses from 2004-09, the period covered by the study, were along the Gulf of Mexico, where coastal wetlands form a crucial buffer against storm surge floodwaters during hurricanes. They have been battered by decades of erosion and salt water intrusion caused largely by flood-control projects and development. Atlantic coast acreage also dropped substantially.

Replacing wetlands is a primary goal of an Obama administration program called the Great Lakes Restoration Initiative that is focusing on the region’s biggest environmental problems. Separately, the U.S. and Canada signed an agreement last year to upgrade the lakes’ water quality that calls for boosting wetlands.

“If there’s a cure-all for the Great Lakes, wetland restoration is just about the highest on the list as anything gets,” said Cameron Davis, a senior adviser with the U.S. Environmental Protection Agency.

Experts said the gains in the Great Lakes region reflected in the study resulted partially from a prolonged drop in water levels, which created new wetland areas as vegetation sprouted along shorelines in places that had been submerged. Some of that acreage could disappear if the lakes rise again in coming years, said Tom Dahl, a scientist with the U.S. Fish and Wildlife Service and one of the report’s authors.

Great Lakes coastal wetlands also face continuing development threats. Many are along shorelines that would be prime locations for hotels or condominiums. Regulations designed to protect them have drawn legal challenges from critics who say they stifle economic growth and violate property rights.

“It’s important to make sure that we don’t resume losing wetlands to a greater extent than we can restore them,” said Susan-Marie Stedman, a NOAA biologist who wrote the national report with Dahl.

As those battles continue, other government programs encourage voluntary wetlands restoration through means such as flooding unused cropland.

The U.S. Department of Agriculture’s Natural Resources Conservation Service has worked with landowners to revive over 40,000 wetland acres in Michigan alone since 1995, spokesman Brian Buehler said.

“Regulations slow the loss. But if we’re going to turn the tide and have a net gain, we need to re-establish wetland acres,” said Jim Hudgins, who coordinates such projects for the Fish and Wildlife Service. “We can work with people to maintain the values and functions of wetlands in ways that benefit the landowners.”

One such project is Erie Marsh, a network of wetlands, farm fields and open water along Lake Erie’s North Maumee Bay. The Nature Conservancy bought the property from a private hunting club and is working with Ducks Unlimited to improve natural features that make it hospitable for waterfowl and fish.

Culverts, gates and other infrastructure are being installed to re-establish a connection with the bay that was cut off decades ago by construction of dikes. Group leaders hope the project will be completed by 2017, enabling fish to reach the wetlands for spawning and foraging.

Farther up the coast, the Fish and Wildlife Service has bought dozens of acres of corn and soybean fields that will be partially flooded to create wetlands and prairie, becoming part of a wildlife refuge covering 48 miles along the Detroit River and Lake Erie.

“You look at it now and wonder how it could be a wetland,” Ducks Unlimited conservation programs manager Jason Hill said, surveying a snow-covered field on a recent afternoon. But once the water level rises, it will teem with swamp vegetation, aquatic birds and critters such as muskrats and snakes — all within a half-hour’s drive of the Detroit metro area, where millions rely on the river and the lake for drinking water.

“Having functioning wetlands in urban areas is good for migratory birds and endangered species … but it also improves water quality for people,” Hill said.