Britons have been warned of 48 Spanish beaches to avoid when on holiday this summer after being given "black flag" status.
A report by the environmentalist group Ecologists in Action found that dozens of beaches are unsuitable for tourists due to toxic chemical spills, dog filth and invasive developments.
Britons travelling abroad this summer have been urged not to visit the beaches in order to avoid disappointment.
Warning of the impact of Spain's dog-friendly beaches, it says that some areas have been ruined.
The Black Flag status can be granted for a number of different reasons
It brands A Calzoa, in the north of the country, "worst dog beach in Spain".
According to local media, the beach has become "a sandbox for dogs" with owners failing to clean up after their pets.
Ecologists in Action warned: "Walking dogs through natural environments has become a very popular activity around the world, which raises a series of environmental problems and challenges that must be addressed responsibly by administrations and society."
It also found that beaches in Malaga, the Canary Islands, Catalonia, Balearic Islands and Basque Country were not up to standard.
Of the 48 black flags awarded, 17 were granted for over-development of the coastline, and 12 were for spills, faulty sanitation system and serious purification problems.
Six of the black flags were due to chemical, light, or sound pollution, another six were due to the impact on biodiversity, three were for litter, and two were due to dredging.
While the Ecologists in Action's black flag status is not an official grade, it has long been seen as a good indicator for tourists of which beaches to avoid.
The group also said that it could have granted black flag status to more beaches due to the poor state of Spain's coastline.
However, its rules do not allow more than two beaches in any region to be given the unwanted marking.
"These are not all the beaches that deserve them, which unfortunately could be more," the group's report said.
"One of the problems is the touristification and urbanisation of the coast."
