Following a pollution incident over the weekend, North Somerset Council and the Environment Agency have advised against bathing at Uphill & Weston beaches.
Wessex Water have been carrying out repair work on a sewage pipe that was leaking underneath the River Axe.
One of Weston-super-Mare's beaches has failed a water standard test for the first time in 30 years.
The quality of water at Uphill Slipway was judged 'poor' under European health standards.
It means that it is not always safe to swim there because of the risk of catching bugs that could lead to an upset stomach or more serious conditions for the vulnerable.
The Environment Agency blames the rain over the summer which may have washed excess pollution from roads, farms and sewers into the sea.