The nearest beach is on the freshwater lake at Puivert (above) only 15 min drive away. It has good facilities including a diving pier, showers, tennis / basketball court and snack bar (the food is excellent and you will need to book to eat there in the evenings as it is so popular!)
A little further (30 min) is Lac de Mont Bel (above). This is a man made lake of 550 hectares set in a stunning spot with views of the Pyrenees. It has a beach, marina and is a mecca for the water sport enthusiast. A must visit while you are here!
There is also a mountain lake at Belcaire. Beautiful on a sunny day with a picnic....
The beaches on the Languedoc coast near Perpignan are only an hour and a half drive away. The best beaches are at Argel sur Mer but there are many others. Click here for details of the beaches you can visit together with their facilities and reviews.
There is a public pool at the leisure centre in Quillan, but you would probably be better advised to visit the pools at Either Axat or Alet les Bains (there is a medieval abbey here which is well worth a visit in its own right). Both are approximately 20 min away.