A helicopter sprayed weed killer over the Mentor Marsh Tuesday.
The goal is to kill tall, thick phragmites, an invasive plant that chokes out native plants.
Some neighbors said they think the spray drift poses a potential health risk.
The spray, called Aqua Neat, contains glyphosate, the same chemical used in the household yard spray Roundup.
The Cleveland Museum of Natural History said the spray is safe and approved by the EPA.
In a statement from the museum, they wrote that eliminating the destructive plant will allow "native plants and wildlife to thrive."
Not all neighbors are concerned about the spray drift near neighborhoods.
Beth Rush, who walked in the marsh Tuesday with her grandchildren, said she wants the marsh restored to the way it looked before phragmites took over.
"Back to the way it's supposed to be, not with that phragmites taking everything over, I’d like to see the flowers, cat tails and trees comeback,” Rush said.
The Mentor Marsh covers 700 acres.