But over the weekend, those who back the plan began to marshal their forces via social media.
"The opposition to the project has spread their message far and wide and threatens to halt the project completely," wrote Gretchen Helmreich, president of the neighborhood association.
"Please help us to move the project forward."
The Horner Park Advisory Council, which has been championing the riverbank restoration project for more than a decade, also reached out to its constituents.
"In the last week, a group of citizens on the east side of the river has raised opposition to this plan because of the degree of foliage that must be removed to accomplish the larger goal of creating a safe and sustainable riverbank," read a statement from Peter Schlossman, president of the advisory council.
Yet the Army Corps of Engineers, which is overseeing the restoration, addressed residents' major concerns after two community meetings, Schlossman said.
The number of upland trees slated for removal has been reduced, grading of the shoreline will be adjusted to preserve large trees, a nature trail near the river's edge has been added to the plan, and a mowed grass buffer near the park's baseball fields has been widened, Schlossman said.
"As president of the Horner Park Advisory Council, I support the project as amended."
Both Helmreich and Schlossman urged people to contact everyone from Sen. Dick Durbin to Mayor Rahm Emanuel to Michael Kelly, general superintendent and CEO of the Chicago Park District.
At community forums held Sept. 9 and Thursday, residents who live along the east bank opposite the park — including Illinois Attorney General Lisa Madigan — outnumbered residents from the west bank by as much as 4-1.
A number of these "West Siders" said that they felt too intimidated to speak up in favor of the project.
Lauren Umek was one of the few who stood up for the restoration.
"Both groups see themselves as hard-core environmentalists," said Umek, a doctoral student in plant biology and conservation. "But the people who have studied" the riverbank restoration for years — Friends of the Parks, Friends of the Chicago River, the Illinois Department of Natural Resources — "are all in favor of it."
Ald. Deb Mell (33rd), whose ward includes Horner Park, also has stated her support for the restoration.
"I would like to see it go forward," she said. "I think it's for the greater good."
The Army Corps of Engineers has indicated it will release its final version of the restoration plan Monday.