It happened at around 3.50am on Thursday morning at Abbey Fisheries, Gowthorpe.
North Yorkshire Police believe the fire was started deliberately.
Officers want to speak to a man who was seen leaving the area who they believe sustained serious burn injuries.
They want to trace him to check on his welfare and because they believe he may hold information vital to the investigation.
Anyone who has any information which would assist officers to locate the man is asked to dial 101, select option one and pass the information to the Force Control Room, quoting reference NYP-21032019-0043.