South East Rivers Trust (& the Wandle Trust)

Help us track down pollution on London’s rivers

Did you know the drainage system servicing most of Greater London is formed of two sewers?

One is the Surface Water Sewer – conveying rainfall from roofs, roads and other hard surfaces straight into the nearest river.

The second is the Foul Sewer – transporting wastewater from toilets, showers, washing machines etc. to a sewage treatment works to be treated before being released into a watercourse.

Unfortunately, sometimes appliances, such as a toilet, can end up misconnected – meaning they have been incorrectly plumbed into the surface water drainage system. This means that foul water is flowing straight in to rivers untreated, instead of to the sewage treatment works. You can see a diagram of this here.

These misconnected outfalls often go unnoticed and can become a chronic source of pollution.

What is an Outfall Safari?

The Outfall Safari method involves systematically surveying the entire length of a river to identify and locate these misconnected outfalls. This allows the pollution to be reported to Thames Water and the Environment Agency so that it can be tackled.

Until the first Outfall Safari was carried out on the River Crane, there was no method for surveying and prioritising polluting outfalls. It’s been so successful that Outfall Safaris have now been carried out on many of London’s rivers, including the Hogsmill.

How can I help the problem?

  1. Check your property for misconnections. Find out how at
  2. Report polluting outfalls via the Environment Agency hotline: 0800 807060

With thanks to: