One appliance and crew from Newport Pagnell, two from Broughton, one from West Ashland, one from Aylesbury, one from Harrold, one from Banbury and three officers attended.
The fire was in two adjacent fields. Firefighters used a drone and extinguished the fire using haydrags, beaters and water from the River Great Ouse.
The last crew left the scene at about 8pm. The cause is currently believed to be a barbecue.