The Nisqually River gnaws away on big rocks pushed into place the last time it took a chunk out of this dike, trying to reclaim its natural route.

Pretty soon, it will get its way.

Managers of the Nisqually National Wildlife Refuge will take the dike out for good as part of a $15 million estuary restoration project 12 years in the planning. With it will go the Brown Farm Dike Trail that provides a 5.5-mile walk along the outer perimeter of the refuge.

A farewell walk for the trail will be hosted for the public today.

The trail will be closed for good May 3, in preparation for a summer of heavy excavation to take out the dike and welcome back the tide, sometime this fall.

In all, project managers hope to restore 762 acres of estuary habitat at the 3,000-acre refuge that were converted to upland pasture and freshwater wetlands when farmers exiled Puget Sound from this place by building dikes to farm the land.

Estuaries are critical places, where fresh water and salt water meet, providing food and shelter for a diverse array of plants and animals. Yet more than 80 percent of the original estuary habitat in the Puget Sound area has been lost to diking, draining and development.

This project, led by a range of partners including the Nisqually Tribe and South Puget Sound watershed groups, is the largest estuary restoration under way in the Pacific Northwest.

The partners hope to boost by 50 percent the amount of functioning, healthy estuary habitat in the South Sound.

The dike trail was created in 1974 when the refuge was opened. And for the more than 180,000 people – many of them birders – who visited the popular refuge last year, its loss cannot be overstated.

“To restore Puget Sound and the Nisqually watershed we are making a big leap, and it is hard to give up the trail,” said refuge manager Jean Takekawa. “It’s been what people know of Nisqually and of the refuge. But I hope people can see and understand there’s another Nisqually that is the land, a living and breathing estuary.”

There are other consolations: A heavily used one-mile boardwalk trail near the refuge headquarters will remain open throughout the project, and isn’t being replaced or changed. A new dike protects the headquarters.

The trademark twin dairy barns at the refuge, built in 1934, also will be untouched.

In 2010, the refuge also will provide a trail that doesn’t exist today, creating at the northwest corner of the delta a nearly three-mile path to allow visitors to walk through the restored estuary on an elevated boardwalk to the mouth of McAllister Creek.

The refuge will maintain 246 acres of freshwater wetlands inside the newly configured dike as a refuge for freshwater birds and wildlife.

The refuge restoration also will include replanting of a 34-acre surge-plain forest that used to thrive under the influence of both fresh water from the river and salt water in the estuary, providing a uniquely complex habitat used by songbirds and amphibians.

Chinook salmon are expected to use the tidal channels that once more will be claimed by the Sound. They are sheltered, food-rich places where young salmon can hide, rest and feed.

Allowing the Nisqually River and McAllister Creek to meander naturally across their flood plains, instead of being constrained within dikes, will provide better floodwater protection for the entire watershed and make the watershed more adaptable if sea levels rise.

About 70 percent of the main stem of the Nisqually River already is protected from development, and the work of earlier conservationists, who blocked conversion of the estuary to a mega-port facility in the 1970s, makes restoration of the estuary possible today.

While more than 1,000 acres of the estuary were diked to create farmland by the early 1900s, the land never was filled or paved, and the old tidal channels are still there, to be reclaimed by Puget Sound.

“This was going to be asphalt and cement as far as the eye could see, but citizens recognized that wasn’t the right thing for something so special. It’s a great community story of people realizing, more than 20 years ago, they could make a difference,” said refuge manager Takekawa. “That’s why restoration can happen here today.”

What: “Farewell Trail Walk” of the Brown Farm Dike Trail

When: Today, 9 a.m. to 3 p.m.

Where: Nisqually National Wildlife Refuge

Details: An opportunity to walk the 5.5-mile trail before it’s removed for restoration work. A shuttle will run along the trail for those who don’t want to walk the whole length.

Cost: The walk is free, but there’s a $3 entrance fee to the refuge.

More information: 360-753-9467 or www.fws.gov/Nisqually