Swimming in december in Alicante, Barcelona, Lloret de Mar, Malaga, Salou, Valencia, Almeria, Benidorm, Cartagena, Costa del Sol, Gibraltar, Marbella, Nerja and Torremolinos is possible... with a wetsuit! Indeed, the water is cold at this time of year with an average temperature of 63°F (min: 59°F/max: 66°F).