A boat and two vehicles were destroyed by arsonists in an attack on an outbuilding in Houghton on Thursday.
Crews from Huntingdon and St Ives were called to reports of smoke near Green Lane shortly after 3pm.
A spokesman for Cambridgeshire Fire and Rescue Service said: “Firefighters wearing breathing apparatus used jets to tackle a fire in an outbuilding that had spread to involve a boat and two vehicles.
“A small cylinder was involved and this was cooled by firefighters.”
Crews remained at the scene for more than two hours.
An investigation revealed that the cause of the fire was deliberate.
Anyone with information should contact police on 101 or Crimestoppers, anonymously, on 0800 555111.