The "Mar de Plastico" or sea of plastic, is a dense conglomeration of plastic-roofed greenhouses on the dry coastal plain of Southern Spain that covers some 30,000 hectares. During the winter months, much of Europe's vegetables are grown here and then transported north by truck. Protected to the north by the Sierra Nevada, the highest mountains on the Iberian Peninsula, the climate here is Southern Mediterranean, and similar to North Africa, and the proximity to the sea and near-constant sea breezes keep temperatures moderate. Intensive irrigation from the subterranean aquifers has created a water shortage, but the greenhouses retain much of the artificial humidity, and many of the plants are grown hydroponically with recycled water. The primary crops during the winter months are tomatoes, sweet peppers, cucumbers, and eggplants (aubergines).