Lincolnshire Fire and Rescue strongly believe that a discarded cigarette was the cause of a grass fire in Hartsholme Park.
Plumes of smoke filled the air around the park on Friday and four fire crews were sent out to tackle the grassland blaze.
Afterwards investigators from Fire and Rescue were dispatched to find the cause.
A spokesperson from Lincolnshire Fire and Rescue said: “The cause is most likely to be from carelessly discarded smoking materials.”
A warning was issued earlier in the week following a number of grassland fires in the county, also believed to be caused by cigarettes.