"It's all over the place," said Tony Whelan, chair of the group. "There's a big motherload down at the aqueduct."

Whelan described the river keepers as being on "high alert" last week after he first discovered the water lettuce in the river when checking on the status of the duck weed problem.

Water lettuce, a foreign plant native to tropical areas that is sold at most garden centres, could potentially kill the river because of its quick reproductive cycle. If left unattended the water lettuce would quickly spread over the surface of the river and choke it out, stealing all the oxygen, said Whelan.

Whelan, along with vice chair Jeff Carl, have been scouting the river routinely, manually removing the water lettuce.

He expects about two to three more trips before every trace of the plant is removed from the Welland River.

Water lettuce floats on the surface and resembles a flower with green leaves, giving it its namesake.

It quickly reproduces however, spawning nine stolons, or offspring, which can then quickly reproduce nine more. Water lettuce also drops seeds below the surface which spawn new plants after the winter.

Whelan said the consequences could be deadly for the vegetation and wildlife that depend on the river, including perch, pike, sunfish and walleyes, as well as herrings, geese and ducks.

So far, said Whelan, the majority of the water lettuce has been found around the aqueduct. None has been spotted at a point further than the Riverview Bridge at Lincoln Street and River Road, said Whelan.

The plant was first found in the Welland River in 2004. It is unknown if the plant can survive Niagara's winter climate.