Firefighters are urging landowners to stop "controlled burning" immediately after a moorland blaze diverted resources away from supporting the response to the coronovirus crisis.
Crews have been dealing with a "mile-long fire-front" at Deer Hill Reservoir in Marsden, West Yorkshire.
They were called to the blaze, believed have been caused by controlled burning that spread, at about 12:30 GMT.
A fire service chief said he was "disappointed" with what had happened.
Nick Smith, assistant chief fire officer with West Yorkshire Fire and Rescue Service, said the blaze could "so easily have been avoided" and called on landowners to change their ways.
"Controlled burning can easily spread, and tackling the consequences takes up a huge amount of the fire service's time and resources - moorland fires can quite literally go on for miles and days," Mr Smith said.
"These are unprecedented times and we require our resources to support communities and help the vulnerable, rather than having firefighters tied up for days on the moors undertaking this kind of arduous work."
The fire service plans to contact landowners about the practice, which involves deliberately starting fires under controlled conditions to clear out low-lying flammable material.
Controlled burning is often carried out on moorland estates managed for grouse shooting, with those in favour of the practice claiming it can prevent fires.