Faecal matter may not always be visible to the human eye but scientists working on Spain’s beaches have found it to be the biggest pollutant in both sand and seawater.

“Faeces and urine that aren’t treated in waste management plants before being poured into the sea are the biggest human pollutant,” Miguel Delgado, head scientist at Spanish epidemiology and public health consortium CIBERSEP told Catalan daily La Vanguardia.

This happens mainly when heavy rainfall in cities washes the waste out of the sewage system and drives it towards the sea.

Serious health issues caused from exposure to bacteria from faecal matter on Spanish beaches have not yet been detected but experts do point to an increase in cases of gastroenteritis and ear infections during the summer period, when more people head to the beach.

Other health problems can include respiratory difficulties, skin infections and eye soreness.

Barcelona authorities are currently carrying out regular tests on their city beaches to ensure the quality of the seawater is high enough for bathers to not face any problems.

“For the past ten years, water quality in 95 percent of Catalonia has been excellent, ten points above the average in the EU,” Mariona De Torres, responsible for coastal waters in Catalonia, told La Vanguardia in an attempt to put the issue into context.