Damage that led to metre River Avon drop to cost £3.5m
Millions of pounds will have to be spent to replace the sluice gates which control the water levels on the River Avon that runs through Bath.
One of the gates at Twerton stuck open at the beginning of October, causing the river to drop by almost a metre.
Some boats were left hanging on their moorings by their ropes.
The Environment Agency said the situation was "frustrating and dangerous" and eventually used a crane to close the gate.
The total cost of replacing the gate is likely to be about £3.5m, the organisation said.
Robbie Williams, the operations manager for the agency, said: "Unfortunately it did jam open, not fully open, but partially open that meant we couldn't control the water levels.
"It wasn't just frustrating for them - it was dangerous. Boats could have got left hanging a metre on their ropes," he added.
Some of those living on the river said that they were not warned early enough of the problems.
"First time we were informed it was too low and too dangerous to manoeuvre," said one resident, Rob Child.
"So it was just a case of sit tight, let the ropes out and hope it didn't do any damage."
Mr Williams said they needed to work quickly to close the gate but said they would learn from their mistakes.
"There was a period in the early evening when things needed to be done quickly. That's really important.
"There's things to be learned because that could be done better next time, there's no doubt about it."
The Canal and River Trust said it was "very sorry" some boats were left "stranded" in the river.
The organisation is talking to the Environment Agency to "fully understand" the issue.