A 55-mile section of Britain's longest canal could close for a month unless there is significant rainfall.
From 30 July, the Canal and River Trust will close locks along the Leeds & Liverpool route amid water supply concerns.
While the closure will prevent boats travelling from Wigan, through Lancashire, and up to Gargrave, near Skipton, the towpath will stay open.
The trust said the closure is likely to last throughout August.
Trust spokesman Daniel Greenhalgh said it had been "a difficult decision" to close the canal, and that it had been working with boating businesses to offer alternative routes.
Sarah Toole, who often visits the canal at Barrowford in Lancashire, said it was a "necessary evil" to maintain water levels.
But Martin Cleaver, who runs a day-trip boat on the canal at Foulridge near Colne, said tourism would suffer.
He said: "We pass 10 or 12 boats a day, that's quite a lot of people on holiday, and when you're on holiday you spend money.
"If you've hired a boat and want to travel on the canal, you can't do and the knock-on effect will be for the pubs, where boats pull in and have a meal."
Canal and River Trust's tips to help conserve water
- Share locks where possible and make the best use of the water available
- Ensure paddles are fully closed once you have passed through a lock
- Aim for minimal contact when navigating through locks by ensuring gates are fully open as you pass through
- Avoid pushing gates open using a boat - this can damage the gate lining, increasing its leakage