The pool is fitted with a cover. This is a safety function and the cover should be closed when the pool is not in use.
The cover has two fixed panel and three sliding ones. To slide cover first remove the gable end panel. Then ensure all the fixings for the first 3 panels have been removed. It is the possible to push the panels under the two fixed panels. Note that only two of the movable panels will go under the end panels so you must stop when the sliding panels meet with the end gable.
For more in for see here http://www.abrisud.co.uk/semi-sliding-pool-enclosure/sliding-pool-enclosure