Beaches in eight counties pose a pollution health risk after sewage was discharged into the sea following heavy rain.
The charity received the data from water companies - whose data showed sewage had been discharged from Monday after wet weather interrupted a heatwave.
Hugo Tagholm, chief executive of Surfers Against Sewage, said: “Whilst the government has shelved the publication of the promised and long-awaited sewage action plan, the industry has reverted to type, pumping and dumping as soon as rain hits.
“Our rivers and beaches are once again treated as open sewers… Our rivers and beaches should not be subject to this type of industrial environmental vandalism.”
The majority of the 50-odd beaches impacted are on the south coast where Southern Water is one of the water companies responsible along with Wessex Water and South West Water.
A spokesperson for Southern Water said: “[The] thunder storms brought heavy rain which fell onto parched ground and couldn’t absorb surface run-off, meaning that more rain than usual overwhelmed our network.
“This led to some overflows – which are used to protect homes, schools, businesses and hospitals from flooding – spilling excess water into the sea.”
They said the discharges are “heavily diluted and typically 95 per cent of them are rainwater,” while they are also looking to reduce rainfall entering sewers.
Last year the company was fined £90million for dumping sewage into the south coast - although the discharges are discouraged rather than illegal.
Sewage dumps are supposed to only happen in exceptional circumstances, although there were 400,000 spills in the UK in 2020 and 2021.
An Environment Agency spokesperson said: “We publish daily pollution risk forecasts throughout the bathing season via the EA’s Swimfo website to indicate when bathing water quality may be temporarily reduced due to factors such as heavy rainfall, wind or the tide.
“The current risk of surface water flooding reinforces the need for robust action from water companies to reduce discharges from storm overflows. We are monitoring the current situation and supporting local authorities where needed.”