WILTON — Wondering what that red stuff is in the Norwalk River at Schenck’s Island? It’s not litter, so people are asked to please not disturb it.

What it is is podostemum ceratophyllum. Come again?

It’s hornleaf riverweed, an aquatic plant that has been reintroduced to the river after being extirpated — destroyed — at least a century ago. The plant is critical for the health of the river’s fish and insects and ultimately the waterway itself.

Kelly Nealon, a graduate student at Western Connecticut State University, and her professor Tom Philbrick, have been in Wilton reintroducing the plant from two other sources in the state. They are working with volunteers from the Mianus chapter of Trout Unlimited in partnership with the town.

Once thought to be in the river, the plant has disappeared, likely a victim of dams and environmental changes over the years. At one time, the Norwalk River had 20 dams used for industrial purposes.

Nealon, who is completing the first year of work toward a master’s degree in integrated biological diversity, said the project has the possibility to help both the fish and the river itself.

“There’s no known occurrences of this species in this location,” she told Hearst Connecticut Media. “As far as we know it does not occur here. It’s possible it occurred years ago, but likely after the were dams put in, it kind of just died out. It’s a common theme in other rivers in the area.”

The hornleaf riverweed is considered a foundation species in rivers in the eastern part of North America, but it is on the decline throughout much of its range according to an article on the website science.direct.com.

It is an aquatic flowering plant, Nealon explained, that attaches to rocks in river rapids.

“It’s a habitat for invertebrates, which helps fish populations because they eat invertebrates,” Nealon said. “It can also provide habitat for fish and it plays a significant role in water quality and river ecology.”

It does that by removing from the water nitrogen, phosphorus, calcium, zinc and other elements, while at the same time contributing important organic matter.

Introducing the plants

Nealon and Philbrick are using three methods to introduce the plant, which they are transplanting from the Little River in Oxford and the Eight Mile River in Old Lyme.

The first method involves attaching root fragments of the plant to rocks with plexiglass bars. The bolts used to hold them in place are red, hence they can be seen through the water.

“The idea is the roots will continue growing onto the rocks,” she said, and then measure how quickly they attach, if at all. “That would be important moving forward if we do it somewhere else,” she said.

The second method employs cages made of plastic mesh into which they will put one rock that has the riverweed growing on it between two clean rocks from the Norwalk River. The hope is the riverweed will spread and grow on the clean rocks. If that happens, the cages can be removed and the rocks will stay in the river.

For the third method, rocks that have riverweed growing on them will have half of it scraped off before being placed in the river.

Anglers fishing the Norwalk River and others who may come upon these unusual-looking bundles of rock and riverweed are asked to avoid stepping on or disturbing them.

Nealon refers to each introduction method as a replicate and said 15 of each replicate will be placed at two locations in the river.

She and Philbrick will return to Wilton throughout the year to study which methods of reintroducing the riverweed work best.

“The idea is to monitor [the replicates] through two summers,” she said. “By the end of next summer we are hoping to see success.” If they are successful, they will remove the cages and plexiglass and leave the plants in the river.

If the riverweed flourishes, it will be a further reinvigoration of this section of the river that has benefited from extensive restoration efforts over the past several years.