Arsonists are believed to have set fire to changing rooms in a park in Portslade in the early hours of this morning.
The blaze destroyed the contents of a storage room and damaged the roof.
Sussex Police began an investigation into the incident after being called by East Sussex Fire and Rescue Service at around 12.30am today (Thursday 11 November).
A spokesman said: “The fire in the storage room of a changing block facility caused damage to the interior and roof and destroyed the contents inside.
“At this time it is not known what items were damaged during the fire.”
Anyone with information is asked to contact Sussex Police on 0845 6070999 or the independent charity Crimestoppers anonymously on 0800 555111.