Three fire crews extinguished a large fire at Hartsholme Park off Skellingthorpe Road.
They were called to the fire shortly after 8pm and the blaze was giving off a lot of smoke.
Anyone in the local area was advised to shut doors and windows.
The City of Lincoln Council said: “The fire was centred on the play area which is currently under refurbishment.
“Unfortunately we believe contractors’ equipment or materials are involved.
“We are extremely grateful to the fire service for their prompt response and thankful that they have been able to prevent the fire’s spread.
“The fire is now extinguished and we will be investigating in the morning.”