Environmental officials are banking on the construction of a bridge or culvert at Grey Cloud Slough to restore its ecological balance.

The South Washington Watershed District is moving ahead with plans to build a bridge or culvert to replace the earthen dam under County Road 75, which has long served as the only road to the north end of the township, officials said.

That move, they hope, will restore the natural flow of water in the slough, a narrow 2.8-mile channel of the Mississippi River, allowing for the "unimpeded movement of fish and aquatic organisms" while improving water quality, according to a 2011 feasibility study.

The township, with its 300 or so residents, is actually two islands connected by the road over the dam.

Last month, the county gave its blessing to the plan to replace the dam with a bridge or concrete culvert. The $1.6 million project, which will be overseen by the watershed district, will involve repaving the road and raising it by a foot to protect it from flooding, and in turn improve "breeding habitats for key fish and other wildlife," said County Engineer Wayne Sandberg.

"Anytime that you're working in the river, you have to be very sensitive to the ecology and the environment," Sandberg said.

Complicating matters somewhat is the fact that the road is heavily used by trucks traveling to and from a limestone quarry on the north island, the largest such operation in the county, Sandberg said. The south island is also home to a sand-and-gravel pit.

In recent years, officials have grappled with how to clean the channel, which is covered by a thick soup of algae that blocks sunlight and robs the water of oxygen, suffocating aquatic wildlife. If left unchecked, environmentalists say, the channel could someday turn into a swamp.

Allowing the water to flow out of the slough should avert that outcome, officials said.

"Hopefully, restoring the flow will help take care of the nutrients that build up back there," said Molly Shodeen, a hydrologist with the state Department of Natural Resources. "During a flood, you'd get a higher degree of flooding of the system there rather than having it stagnant."

Watershed district officials did not return calls for comment.

Severe flooding in the region in 1965 prompted officials to fill the previous culvert with dirt, creating a dam to impound the waters of the slough. Little consideration was given at the time to the ecological consequences, the study said.

Most officials are leaning toward the bridge option because it would also allow recreational boats to pass along the slough. But some favor building a culvert, which they claim is the more cost-effective option.

Township Supervisor Dick Adams said he supports building a culvert "because I can't believe that it's the same price as the bridge. I absolutely can't believe that it's not a more economical option. ... All the agencies are in favor of it. It's just a matter of coming up with the funding."

According to officials, the project will be paid for with $500,000 in county gravel tax dollars and $800,000 in watershed district funds. The rest of the project will be funded through grants.

Shodeen, the hydrologist, remains skeptical that the project will have as immediate an impact on the slough as officials envision.

"I'm not convinced that one of the causes for excess nutrients might not be septic systems, so it will probably be worth looking at whether the septic systems along the channel there are in good shape," she said.