A team of Royal Academy of Engineering scientists say the risk from human faeces is increasing.
Human faeces in our rivers is putting the public in danger and the risk will increase without action, the UK's top engineers and scientists have warned in a report.
The report led by the Royal Society of Engineering called for an upgrade of the UK's sewage system and more widespread testing of the country's waterways.
Prof Chris Whitty - the UK's chief medical officer - said it was a "public health priority as well as an environmental one".
The government said the largest infrastructure programme in water company history was currently taking place.