The public boat launches on the Houstonic River's three big lakes -- Candlewood, Lillinonah and Zoar -- have clear signs of warning: Beware of zebra mussels.

Now the public education effort may move north, up river.

That's because there's increasing evidence zebra mussels in their nymphal stage exist along the length of the river in Connecticut.

People kayaking and canoeing in the river could carry those nymphs -- called veligers -- to other bodies of water unless they're warned to clean their boats.

"It's not a question of whether anymore,'' Lynn Werner, executive director of the Housatonic Valley Association, said about the need for education along the river. "It's a question of when.''

At a recent meeting of the Zebra Mussel Task Force -- a group of town officials and lake advocates formed in 2010 after the adult mussels were found in Lillinonah and Zoar -- Gary Smolen of FirstLight Power Resources said the utility's own monitoring efforts found veligers at two of the company's hydroelectric power plants: in Falls Village and at the Rocky River power plant in New Milford.

Inexplicably, Mr. Smolen said, the veligers haven't been found yet at the Bull's Bridge power plant near the Kent-New Milford town line -- the plant that lies between Falls Village and New Milford.

Those results match the findings of Ethan Nadeau of Biodrawversity, an Amherst, Mass., research company.

He found the mussels in Lillinonah and Zoar in 2010. This year, Mr. Nadeau said he's found the veligers in the Housatonic River itself.

People have mobilized to stop the spread of the mussels because the inch-long, non-native bivalves -- they come from the Caspian Sea -- have proved to be highly invasive in North American waters.

The mussels reproduce with great rapidity.

Once they begin to colonize a water body, they overtake native species and alter the water system ecology. They also can quickly cover docks, boat hulls and water intake pipe with their small, sharp shells.

To combat their spread, the task force has organized a system of volunteers who go to boat launches to tell people about the menace posed by the mussels and the need to decontaminate boats after they've been in a body of water where the mussels live.

They also have erected educational signs at Candlewood, Lillinonah and Zoar to tell boaters what they need to do. Meghan Ruta, the HVA's water protection manager and a task force member, said recently the signs and educational pamphlets need to be distributed north along the Housatonic.

Ms. Ruta said, across the border in Massachusetts, the HVA is very involved in zebra mussel education.

That's because Laurel Lake in Lee, Mass., in now infested with the mussels. Because a brook from the lake leads to the Housatonic River, it's suspected Laurel Lake mussels may have spread into Connecticut.

Ms. Ruta and Ms. Werner said the HVA is planning a joint meeting of Connecticut and Massachusetts activists this winter to see how they can coordinate their fight against the invasive mussels.

"We want to get behind this thing in a way that will give us the biggest bang for our buck,'' Ms. Werner said.