Untreated sewage was discharged into England’s coastal bathing waters for more than 160,000 hours last year, according to figures collated by the Liberal Democrats to mark the start of the summer sea-swimming season.

Data compiled by the party using Environment Agency figures on 2021 discharges shows that water companies released raw sewage 25,000 times into designated bathing waters off the English coast.

Figures collated by the campaign group Top of the Poops reveal that when also including the bathing waters in Wales, water companies released untreated sewage for 217,804 hours.

The bathing water designations – which were created by the EU – are supposed to highlight the country’s cleanest and safest waters for the public. The quality of the water is publicly identified on signs at the bathing beaches, ranging from excellent to poor.

The longest discharges into bathing waters were carried out by United Utilities, which released untreated sewage into sea-swimming spots in its area for almost 75,000 hours. The company’s worst-hit bathing water site was Morecambe South beach.

Southern Water, which was last year fined a record £90m for spilling billions of litres of raw sewage into Hampshire and Kent coastal waters, was responsible for 20,367 hours of untreated sewage discharges into designated bathing spots off the coast in their area.

South West Water discharged sewage into bathing beauty spots for 43,901 hours, with their longest discharge released at Ilfracombe’s Wildersmouth Beach, lasting 1,833 hours.

The figures were released as the official sea-swimming season opened on Sunday. This marks the start of annual monitoring of bathing-water quality, which helps to inform the public about the water at beaches they visit. The season lasts until September.

Tim Farron, the Liberal Democrats rural affairs spokesperson, said: “It is now or never to save families from swimming in sewage-infested waters this summer.

“Children should be free to enjoy Britain’s great coastlines and lakes, yet Conservative ministers are letting water companies get away with shameful sewage dumps. This is an environmental scandal.”

The data was released as many parts of the UK prepare to go to the polls on Thursday to vote in local elections.

The Liberal Democrats have called for a sewage tax on water companies’ profits to be used to clean up coastlines, rivers and lakes.

Environment Agency data shows that in 2021 water companies released raw sewage into all coastal waters and rivers in England for more than 2.7m hours. The Lib Dems said that in the same year the firms made £2.8bn in operating profits and paid out £27m in bonuses to senior executives.

Hugo Tagholm, chief executive of the campaigning charity Surfers Against Sewage, said: “Water companies are getting away with blue murder – repeatedly dumping raw sewage into areas of special recreational interest, with seeming impunity.

“Our great beach-loving public shouldn’t have to swim or surf the gauntlet 0f sewage, pathogens and pharmaceuticals that are pumped out through water company pipes. Surfers Against Sewage has been challenging the water industry for decades, calling for them to put people and planet before excessive profits and executive bonuses. We demand a new decade of ambition to clean up and protect all our bathing waters and blue spaces.”