“Harbor Wetland,” a National Aquarium floating exhibit that re-creates a salt marsh habitat, will be open to the public Aug. 9, near the date of the aquarium’s 43rd anniversary.

The exhibit, including a walkable floating dock, spans 10,000 feet. Admission will be free, and it will operate the same hours as the aquarium, which is open between 9 a.m. and 6 p.m. from Sunday through Thursday and until 9 p.m. on Fridays and Saturdays. Construction on the wetland began in November.

It took years of trial and error to develop the right technology that would float the habitat, said the aquarium’s director of field conservation, Charmaine Dahlenburg. The aquarium was the first in the country to deploy a floating wetland in 2010. But it was too small to hold the weight of wildlife — geese kept eating the grass, mussels and barnacles grew on it and anchored the structure to the bottom of the harbor.

The aquarium ended the first floating wetland after three years. It came up with the smaller prototype of the exhibit that has been floating between piers 3 and 4 in the Inner Harbor since 2017. Since then, they worked on scaling the exhibit up.

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Engineers were able to add pontoons underneath the wetland exhibit that allowed it to float. Each pontoon has its own valve that allows engineers to control the ratio of air and water, so they can bring the pontoon back up if it starts to sink. They are also hoping to patent the technology and share it with other post-industrial cities, Dahlenburg said.

They also added pilings to the exhibit so that the floating wetland stays put and rides up and down with the tide. They also added shallow water channels running through the center of the exhibit, adding different topography levels, so they can put different species of grass.

The existing prototype floating wetland in the water between piers 3 and 4 was installed back in 2017. (Mark Moody/Mark Moody, National Aquarium)

The harbor is not well understood, and it’s often thought of as a dead zone, Dahlenburg said. But the harbor is only getting better. Throughout the process, the aquarium has documented more than 30 different species of wildlife. Striped bass and blue crabs have swum under the wetland. A mallard built a nest. Night herons, river otters and muskrats have stopped by.

A natural salt marsh habitat thrived in the city hundreds of years ago. There are not many green spaces in the city Baltimore residents and visitors can go to, and many do not have access to the harbor.

“We wanted to bring these Chesapeake Bay habitats to the residents of Baltimore City to our visitors so they can enjoy it,” she said.

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Volunteers and staff plant grasses on the Harbor Wetland, May 16, 2024 (Philip Smith/Philip Smith, National Aquarium)

Visitors will enter through the gateway and start at the first outdoor classroom, where they can learn about the history of the harbor. As they walk south, there will be another space for a classroom that will focus on the future of the harbor.

Adam Lindquist, vice president of Waterfront Partnership, said the exhibit is “the best example of a floating wetland system” in saltwater that he has seen. While he thinks the exhibit alone won’t charge the harbor, combined with other projects, including oyster gardens and Mr. Trash Wheel, he sees the water quality is improving in the harbor.

“We can’t wait to see what wildlife enjoys these floating wetlands,” he said.