Fire crews have been pumping 3,000 litres of water per minute from the sea at Hope Cove to douse the Bolberry Down wildfire.
Crews are using the lifeboat slipway to run a 1.3km (0.8 mile) hose up to the cliffs to tackle the blaze.
Firefighters are only able to draw water for two hours before and two hours after high tide.
The wildfire, near Kingsbridge, has been intermittently burning for two months.
Devon-based fire crews have been working to make sure the gorse wildfire does not go beyond the coast path.
Firefighters have been assisted by a helicopter paid for by National Trust, being used to dump seawater on the flames in harder-to-reach places.
Landowners, the National Trust, said dry ground and the recent hot weather had probably caused the fire.
Si Carey explains how we are working to prevent the gorse fire on the cliffs at Bolberry Down from spreading. Today firefighters have been using a high volume pump, a flail mower, a helicopter to drop water and the fireboat. Please keep roads in the area clear this weekend for us pic.twitter.com/fJGQytBjQZ
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