GREENE – The leaky 19th-century dam that keeps Allen Pond deep and clean is about to undergo repairs.

Workers plan to lower the pond’s depth next week.

Then, they’ll begin the process of creating a coffer dam and pouring the concrete that will finally fix the aging structure.

“My children and their children swim here,” said Bob Beckey of the Allen Pond Improvement Association. “I want this to be around.”

After years of debate, the group has raised about $3,000 to buy the materials to repair the 140-foot dam, located on the pond’s north end.

The problem is nature.

Though the dam has been in place since at least the 1850s, it couldn’t fight trees.

The roots of an oak on the west side of the spillway reached deep into the dam, leaving trickles of water that have threatened the whole structure, Beckey said.

Plans filed with the state call for the creation of a sandbag coffer dam near the weakened section, said Dana Murch, the dams and hydropower supervisor with the Maine Department of Environmental Protection.

Behind the temporary dam, volunteers from the pond association plan to clear away the fragile sections of the permanent structure. They will drill holes into the ledge beneath and install rebar pins to reinforce the concrete that will follow, Beckey said.

The volunteers will include a stone mason and a heavy machinery operator, with his excavator, to do much of the work.

The entire project, including drilling the holes, building forms and pouring cement ought to take about a week, Beckey said.

During the work period, the dam will continue to spill no less than 80 gallons per minute, Murch said.

Another week will need to pass before the water can be raised again, due to state rules.

When it’s finished, the leaks should be stopped.

Beckey hopes the dam will last for more generations.

His family has lived beside the pond since the late 1940s. However, his research goes back to the 1850s, when it was known as the Brigham Dam Privilege.

Water from the 180-acre pond empties into Allen Stream, one of the few northbound streams in the region.

In Leeds, it empties into the Androscoggin River.