People planning to visit Spain this summer have been hit with a number of warnings if they plan to visit the beach while away.

The Foreign, Commonwealth and Development Office (FCDO) offers guidance for travel to any of 226 nations and territories in a bid to help people make informed decisions and stay safe. Part of its most up-to-date advice for Spain reads: "Every year, people drown in the sea and in swimming pools in Spain.

"Always supervise children, even if they can swim or there is a lifeguard present. Take care when swimming in the sea. Some beaches, especially around Spanish islands, may have strong undercurrents.

"Hidden rocks or shallow depths can cause serious injury or death. Do not dive into unknown water and do not swim at beaches where a river runs into the sea."

It goes on to say: "Many beaches have a flag system. Make sure you understand the system and follow any warnings (a red flag means you must not enter the water).

"Take extra care and get local knowledge if there are no lifeguards, flags or signs. If you are walking along unmonitored beaches, be aware that waves can come in further than expected and have strong undertows."

Earlier this week, a new report showed almost 50 Spanish beaches have been hit with a substandard "Black Flag" rating, due to chemical spills, sanitation problems, and pollution. Popular destinations for UK tourists to be hit with the "Banderas Negras" status include Malaga, Barcelona, and Alicante, as well as parts of the Canary Islands.

A spokesperson for Ecologists in Action said that "touristification and urbanisation of our coastline" was one of the biggest problems Spain's coastline faced.

These are the 48 black flag beaches that tourists are being warned about:

• La Farella, Girona, Catalonia
• Various beaches on the Costa Brava, Girona, Catalonia
• Comarca del Maresme, Barcelona, Catalonia
• Sant Adrià del Besò, Barcelona, Catalonia
• Camino de Ronda, Tarragona, Catalonia
• Playa de la Pineda, Costa Dorada, Tarragona, Catalonia
• Playa de L'Estany-Capicorb, Castellon, Valencia region
• Playa de Burriana, Castellon, Valencia region
• Beaches at the Parque Natural de l'Albufera, Valencia, Valencia region
• Puerto de Valencia, Valencia, Valencia region
• Barranco y playa del Amerador, Alacant, Valencia region
• Playas de Cap l'horta, Albufera, Postiguet and San Gabriel, Alacant, Valencia region
• Mar Menor, Murcia region
• Portman Bay and Sierra Minera, Murcia region
• Playa Quitapellejos-Palomares, Almeria, Andalucia
• Playa de 'El Lancón' en Carboneras, Almeria, Andalucia
• Playa de Castell de Ferro, Granada, Andalucia
• Playa Granada y Poniente, Granada, Andalucia
• Playas de Malaga, Malaga, Andalucia
• Coast of Malaga, Malaga, Andalucia
• Tarifa, Cadiz, Andalucia
• Costa de Trafalgar, Cadiz, Andalucia
• Huelva river, Huelva, Andalucia
• El Portil, Huelva, Andalucia
• Aldán river, Concello de Cangas, Pontevedra, Galicia
• Arousa river and Pontevedra river, Pontevedra, Galicia
• Minera de Galicia, A Coruna, Galicia
• Pereiro river and Ramisqueira river, A Coruna, Galicia
• Alcoa pond, Lugo, Galicia
• Galician coast, Lugo, Galicia
• Port of Figueres, Asturies
• Villaviciosa, Asturies
• Playa de Usgo, Cantabria
• San Román de la Llanilla, Cantabria
• Lamiako marsh area, Bizkaia, Basque Country
• Gernika and Murueta, Bizkaia, Basque Country
• Santa Clara Island, Gipuzkoa, Basque Country
• La Concha Island, Gipuzkoa, Basque Country
• Cala Xarraca, Ibiza, Balearic Islands
• Playa de Talamanca, Ibiza, Balearic Islands
• Port of Melilla, Melilla
• Melilla Bay, Melilla
• Monte Hacho, Ceuta
• Playa de Desnarigado, Ceuta
• Playa Blanca, Las Palmas, Lanzarote, Canary Islands
• Corralejo Dunes, Las Palmas, Fuerteventura, Canary Islands
• La Tejita Beach (Granadilla), Puertito de Armeñime (Adeje), Tenerife, Canary Islands
• Northwest coastline of Tenerife, Canary Islands