The number of monitored bathing waters in England rated as poor and unfit for swimming has more than doubled, from 18 to 37.
More than 400 sites were regularly monitored this summer with 92% of them reaching the minimum standards for bathing, a slight fall from 96% last year.
The Environment Agency – which carried out the testing – says those figures are in part due to 27 new sites being monitored this year, of which 18 were rated poor.
The government called the latest figures “unacceptable”.
Water minister Emma Hardy blamed England’s water companies.
Environment Agency Chair Alan Lovell said the results came against a background of increading demand for bathing sites across the country.
“While overall bathing water quality has improved in recent decades due to targeted investment and robust regulation, today’s results show there is much work still to do, particularly to bring our inland bathing waters up to standard,” he said.
The figures show a notable difference between the quality of bathing sites on the coast and inland.
95% of coastal waters met minimum standards this year, compared to only 53% of rivers and lakes.
The Environment Agency says that’s because salt water can act as a natural disinfectant and the sea naturally disperses pollutants faster.