Earlier this month, signs began appearing pinned to a lock on the Huddersfield narrow canal: “Canel [sic] And River Trust,” they read. “Please leave this paddle up after use. To prevent flooding to properties.”

Over the past few weeks, lock 20W, near the village of Greenfield, has become the source of a bitter row between boaters and homeowners. Canal boaters have been pulling the signs down, only for the homeowners to put them back up again.

Boaters said the low water levels were causing them to run aground, while homeowners said if the lock was not drained, sewage from a nearby pumphouse overflowed and ran into their properties.

“It leaks into the house,” one resident wrote when the row spilled on to Facebook. “The sign is there for good reason.”

Her comment came in response to a post from Adam Byram, who suggested “skullduggery” was at work in the village close to Uppermill, outside Oldham. “Someone keeps putting fake CRT [Canal & River Trust, the charity that looks after the UK’s waterways] signs on the lock and opening the paddles to let the water out,” he wrote, adding that he had been “grounded” in the canal.

“I saw the fake sign on the actual lock and obviously the spelling was ‘canel’ so I knew straight away,” Bryam said. “As I went up, the canal was more or less empty, and I got grounded above where the sign is, in the middle of the canal.

“I had to actually ask a person walking past,” he added. “I threw them my windlass, which is the thing that opens the canal paddles, to the tow path. I was stuck in the middle of the canal, so they went up and they knew what they were doing and they let some water down, so I was able to refloat, and I went on my merry way.

“I don’t really think that a member of the public, without a boat licence or any affiliation to the CRT, should be messing with the locks,” Byram said. “It’s a valuable resource, and if they drain the water, it damages boats.

“Local people have taken it upon themselves to decide what is right and wrong on the canal,” he added. “But when you open one of those [locks] up and it drains the canal, you are losing millions of gallons of valuable resource. Last year, people were stuck on the canals for months because of low water.”

Michelle Beddow-Green, who has lived on the water for nearly three years, agreed. “It’s terrible on the Huddersfield narrow canal because there are always breaches going on, water levels drop a lot, and there’s always a lot of problems.

“It does affect everybody,” she added. “I can’t open my doors sometimes because it drops by that much, you can’t open your hatches. It affects boating life, not being able to get up to over to the Standedge tunnel. It can affect it when boats get breached due to lack of water.”

Another boater, David Murray, said the low water level was a serious problem. “I don’t know how long my boat’s going to stand being smashed on the floor,” he said. “A guy came walking past yesterday and he told me that it was very shallow and they’re struggling to get anywhere because somebody keeps leaving the locks open,” he added, “but who leaves locks open?”

The Guardian found one person willing to admit to it: an 80-year-old retired gardener, whom we have agreed to call Ken. (He did not want to be identified further for fear of reprisals.)

Ken had made the signs on a laminator at his home. And he said he did have a windlass, which he had used to open the lock gates.

A stone pumphouse beside the canal, Ken said, takes all the sewage from the nearby properties. “When that lock’s full for a matter of hours – we’re not on days here, a matter of hours – it floods. And there’s nothing worse than getting sewage coming up [into] your bath.

“And somebody in their wisdom has been coming down and closing the paddle, taking all the signs off that say leave the paddle up, and it’s causing havoc.”

He referenced an official green sign from the CRT, which is pinned to the lock, and said the paddles were supposed to be left open. His own signs, he said, were based on a CRT template, and had been put up because boaters did not notice the smaller official one.

Ken produced one of the laminated signs. “That’s not the one with the spelling mistake on it?” his wife asked, adding, “I’m dyslexic.”

“Why I’ve been putting them up is because we don’t like sewage coming up,” he said. “I mean, that’s the top and bottom of it.”

“It’s been a nightmare all this month,” he said. “I’ll go and have a bath, but I can’t, it is gurgling back, and you flush the loo, and it doesn’t flush. It’s not nice – and it smells.”

The CRT said it had been dealing with an “ongoing issue” at Grade II-listed lock 20W and had “been working hard to resolve the situation for local residents, as well as boaters”.

“When this lock pound is left full, water unfortunately leaks into the cellar of an adjacent cottage, which is part of an old canal wharf,” the CRT said. “Our charity has carried out extensive grouting of the lock wall and installed pumps that automatically remove any water leaks, caused when the paddle is left down and the lock refills over time.”

The CRT confirmed there was a sign on the lock gate that asked boaters to leave the lock empty.

“Additional signage has been ordered and will be fitted on the lock gate balance beam to explain the situation,” the CRT said.

The charity said that rather than lock 20W being left empty, the recent low water levels “have been down to an increased number of boats using the Huddersfield narrow canal, including boaters making their way to attend the 25th anniversary of the restoration and reopening of the 215-year-old waterway, and not from paddles being left open”.

“Our team will continue to monitor the situation, and we’d also encourage everyone to please respect our advice signs, which are in place to keep people safe and protect the canal,” the CRT added.