These operate in a similar way to the above ground covers but the roller is submerged when the pool is open for swimming.
The covers are used throughout the year and keep the pool water clean in winter and stop evaporation and reduce heat loss from the pool water surface in the summer as well meeting the safety laws in France.
This is probably the most attractive looking way to meet the safety regulations - and it is certainly the one that involves the least hassle and maximises the pleasure that you get from your swimming pool:-
These covers start at about £10,000 for the smaller pools - and that does not include a hardwood walkway over the submerged cover like the one above does.
The cover does take up about 1 metre of the pool length and so a pool 1 metre longer is required if swimming space is not to be lost.
These covers are supplied with submerged safety panels that stop swimmers getting under the roller and that also comply with French standard NFP 90 - 308.
There is more information and more pictures of these floating covers in the equipment section of this website.