Swamp tour operator Paul Trahan pointed to the almost motionless water on the West Pearl River on a recent afternoon — a mirror-like surface that reflected ghostly images of the gum and cypress trees lining the waterway.

This time of year, the river is low, Trahan told a group of public officials and media members on a tour organized by the Gulf Restoration Network. High-water marks from spring flooding are clearly visible on the trees.

It's a cycle he's seen over and over again during years of taking tourists out on the water as high water brings nutrients into the swamp and low water allows new trees and other vegetation to germinate.

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A floating shack sits on the Pearl River in Slidell, La., Thursday, Nov. 16, 2017. A possible river damming project in Jackson, Mississippi, would affect the Pearl River including the businesses that rely on the waterway.

But Trahan fears a proposed dam in Mississippi could disrupt that ageless cycle downriver, where he operates Dr. Wagner's Honey Island Swamp Tours. If the low-water period, from about July to December, is too low because of a lack of flow and greater evaporation upstream, it could result in higher salinity, hurting plants and wildlife that live in the West Pearl.

Billed as a flood-control project, the so-called One Lake project would involve dredging and widening the Pearl River and building a weir or low-head dam to create a 1,500-acre lake in Jackson, Mississippi's capital.

The Rankin-Hinds Pearl River Flood Control and Drainage District is the driving force behind the project, authorized through the federal Water Resources Development Act.

Supporters say it will prevent flooding in Jackson, but it's also been touted as an economic development project, and some of the money to study the project — about $1 million — came from the Mississippi Development Authority.

At the lower end of the river system, Louisiana and St. Tammany Parish officials, along with environmental groups, say that the project poses an ecological threat to the river and the vast Honey Island Swamp, as well as to oyster reefs along the coast.

The Pearl River is the fourth largest freshwater source for the Gulf of Mexico east of the mouth of the Mississippi, said Andrew Whitehurst, of the Gulf Restoration Network. Its flow is important to maintaining a balance of salinity for marshes and oyster reefs from the Mississippi Sound through Lake Borgne to eastern Lake Pontchartrain.

It's an argument that's been waged between different interests in the two states for nearly a decade. The Rankin-Hinds flood control district in Mississippi first began pushing for the lake's creation in 2008. Initially, the district sought a far more ambitious two-lake project that was rejected by the U.S. Army Corps of Engineers as too expensive and unfeasible.

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Fishermen fish on the Pearl River in Slidell, La., Thursday, Nov. 16, 2017. A possible river damming project in Jackson, Mississippi, would affect the Pearl River including the businesses that rely on the waterway.

But the district came back with a one-lake alternative in 2013, holding a series of meetings that drew opposition from state agencies in Louisiana and St. Tammany Parish and demands that studies of salinity and water level downriver be included in analyzing the environmental impact of such a project.

The project is under technical review by the Corps, according to Whitehurst — something that's been going on for nearly three years. A draft environmental impact statement should be coming out in December or January, Whitehurst said, and at that point, public comment will be taken and public meetings held.

St. Tammany Parish Councilman Gene Bellisario said the flood control district has agreed to hold one of the meetings in St. Tammany after meeting with him and Councilwoman Michele Blanchard in February.

"We both feel that there's a high probability of adverse impacts on the West Pearl, regardless of what they say," Bellisario said. The project has an economic development basis, he said. "It's not just about flooding."

The Mississippi district is the sponsor of the project and has identified the lake as its preferred alternative for dealing with the threat of flooding, over options like levee improvements and channel modifications or even flood-plain buyouts, Whitehurst said. As the sponsor, it is responsible for the environmental impact statement and public notification.

Officials with the flood control district did not return calls for comment.

The Gulf Restoration Network notes that the study area for the environmental impact statement is restricted by federal law to the metro Jackson area, which the group believes will mean that downstream and coastal effects will be downplayed.

State Sen. Beth Mizell, who was on the tour, said she intends to keep a close eye on developments.

Greg Shaw, a member of the Board of Supervisors for Hancock County, just across the state line, said that he is just learning about the project and wants to know how it will affect oyster reefs and other assets there.

Hancock County, Mississippi, also has asked for a public meeting to be held there when the statement is published, Whitehurst said.

From Trahan's perspective, a lower flow in the river won't prevent his boats from taking people out into the swamp, but he fears it will change what they might see there. He's worried about the ecosystem and the wildlife, including species like the threatened Gulf sturgeon and the ringed sawback turtle. The river is designated as critical habitat for both.

"The best thing that can happen is just to leave it alone,"  he said.

Follow Sara Pagones on Twitter, @spagonesadvocat.