Pollution warnings are in place for almost 50 beaches in England and Wales after untreated sewage was discharged into the sea around the coast.
Official data shows discharges have taken place since Monday and Southern Water says they have been made to protect homes and businesses.
It follows a period of heavy rain across southern England, after a spell of extremely dry weather.
Data was provided by water companies to the Safer Seas and Rivers Service.
The service is run by the charity Surfers Against Sewage.
Many of the beaches contaminated are popular resorts, and include Bognor Regis, Lulworth Cove, Newquay, Seaford and Southend-on-Sea.
The majority are along England's south coast.
Southern Water is one of the water companies responsible for those regions, along with Wessex Water and South West Water.
In a statement, Southern Water said: "There were thunderstorms accompanied by heavy rain the night before last and yesterday [Tuesday]. Storm releases were made to protect homes, schools and businesses from flooding. The release is 95-97% rainwater and so should not be described as raw sewage.
"We know customers do not like that the industry has to rely on these [discharges] to protect them, and we are pioneering a new approach."
Last year Southern Water was fined a record £90m after admitting deliberately dumping vast amounts of sewage into sea across the south coast.
These kind of discharges - which are legal - mostly happen after heavy rain, when there is a risk that pipes, which carry storm-water along with sewage, may overflow.
In a statement, the Environment Agency said that sewage pollution could be "devastating to human health, local biodiversity and our environment". It said it would not "hesitate to act to eliminate the harm sewage discharges cause to the environment".
It has previously called for the top executives of England's water companies to face jail when serious incidents of pollution occur.
Hugo Tagholm, chief executive of Surfers Against Sewage, said: "Our rivers and beaches are once again being treated as open sewers. Years of underinvestment is now in plain sight."
The government has said it intends to produce a plan to reduce storm overflows by 2022. This was made a legal requirement by the Environment Act 2021.