The water company said that in the past 24 hours, raw sewage has been pumped into the sea off beaches including Pagham, Aldwick, Bognor Regis, Felpham and Littlehampton.
Residents are being told that the releases 'may be affecting water quality'.
Last week an amendment from the House of Lords to the Environment Bill which would have placed a legal requirement on water companies not to dump sewage into rivers and seas was voted down.
MPs who voted against the original amendment included Bognor Regis and Littlhampton MP Nick Gibb, and Chichester's Gillian Keegan.
But following a major backlash the government said it would make a further amendment to the bill that will see a duty enshrined in law to ensure water companies secure a progressive reduction in the adverse impacts of discharges from storm overflows.
A Southern Water spokesperson said: “A storm release happens when, in order to protect people’s homes and businesses, schools and hospitals from flooding, water is released through a combined sewer overflow (CSO).
"This usually occurs during periods of heavy rainfall – such as we’ve seen this weekend when up to 20mm of rain fell during the day on Sunday and around 95 per cent of these releases are rainwater.
“We are already acting now to cut pollution incidents by 80 per cent over the next four years and we believe we can achieve a similar reduction in storm released by 2030.
“All 83 of our bathing waters meet strict European standards, a challenge which 20 years ago seemed impossible, but was delivered.
"Now we want to take the next steps which is why we are investing over £2 billion on improving our wastewater network. This investment is on track and is already making a tangible difference in communities across our region.
“Another visible and public example of our commitment to tackle this problem is our industry leading Beachbuoy app. This provides near real-time information on releases of stormwater and is part of our drive to be as transparent as possible.
"This initiative will make it easy for everyone to hold us to account in reducing storm overflows and we are confident our customers will see a real improvement as our investment programme begins take effect.
“In order to go faster and further we are already looking at innovative solutions to reduce storm releases while ensuring value for money.
"We think it is achievable with the right partnerships and collaboration underpinned by policy. The first of these proposals, all incorporating nature based approaches, will be published for consultation in the next few weeks.
“To ensure action happens we have today launched a dedicated task force which will work with customers and regional stakeholders to focus on reducing the number of these incidents as quickly as possible.
"We are certain a holistic approach, working with local government and stakeholders is the way forward to reach the targets we all want to achieve.”