The YMCA Fleetwood fitness centre has been evacuated after a power cut this morning.
The popular Swimarathon event was being held at the time and has now been postponed after participants had to leave the building for safety reasons.
YMCA Fleetwood said in a statement the centre was closed "due to unforeseen circumstances".
Mary Woodman, one of the organisers of the Lion's Swimarathon event, said there had been a power cut after water got into the building.
She added: "There was a power outage in the swimming pool and they had to evacuate the building."
The Swimarathon, which had already started at that point, had to be called off.
She said organisers would now have to see if it would be possible to rearrange the event.