London’s Rivers

Citizen science volunteers

London's rivers are a vital habitat for wildlife and a great resource for people, yet they are degraded by pollution. Please help us health-check and survey our rivers as part of our ongoing programme of Citizen Science projects.

Volunteer to healthcheck London's rivers

Why we are improving London’s rivers

As more people around the world choose to live in cities it is essential that we learn how to accommodate wildlife within urban settings. In London our rivers and streams are recognised as a priority habitat, yet they are currently classified as being in ‘poor’ or ‘bad’ condition. These rivers are not achieving their potential either as habitat for wildlife or as a natural resource for Londoners, and, as such, are in urgent need of our help.

ZSL is engaged in a range of projects that harness the energy, skills and enthusiasm of local communities to help drive improvements in the quality of rivers. Our work is collaborative and brings volunteers from grassroots organisations together with the Environment Agency, Thames Water and fellow NGOs. Please do get in touch if you would like to join us in our work.


I’m a local resident and I noticed there was some pollution in the river and I’m quite interested to find out about the water quality and also the ecology and how we can improve the water quality of the river" - Karolina Allu, Citizen Science Volunteer


The Riverfly Monitoring Initiative


The Riverfly Monitoring Initiative (RMI) is a UK wide citizen science scheme that is used to detect pollution events and learn about long-term trends on river health. ZSL act as the London Riverfly Monitoring Hub, working with project partners to support the development of RMI schemes on rivers throughout the Greater London area.

The RMI is a scheme created and endorsed by The Riverfly Partnership which is a dynamic network of organisations working together to protect river habitats for wildlife and to improve water quality. ZSL are an active board member of The Riverfly Partnership.

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Citizen scientists involved in the Riverfly Monitoring Initiative

Misconnections and the Outfall Safari

Much of Greater London is serviced by two separate drainage systems. One collects rainwater and flows directly into our rivers, and the other takes foul wastewater from buildings to sewage treatment works to be cleaned before being released into a river.

Misconnections between the two drainage systems, often caused by inexpert plumbing, results in pollution pouring directly into our rivers via drains known as outfalls

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Until recently, there has been no systematic surveying of outfalls in urban rivers to identify pollution and notify the relevant authorities. The Outfall Safari is a citizen Science method devised to address this evidence gathering and reporting gap. It was created by the Citizen Crane project team in partnership with staff from Thames Water and the Environment Agency and is. regarded by the Environment Agency as best practice.

The Outfall Safari methodology encompasses the following activities:

  • record and map the dry weather condition behaviour of surface water outfalls in urban rivers
  • geolocate and photograph sources of pollution and report them to Thames Water and the Environment Agency
  • recruit more volunteers to the work of River Catchment Partnerships to help deliver the objectives of catchment management plans 

ZSL has led on the most comprehensive survey of London’s rivers undertaken in recent years. Findings indicate the true scale of the problem of sewage and other pollutants being sent into rivers by homes and business across London due to misconnected plumbing.

PDF icon Tackling Pollution in London’s Rivers (4.92 MB)  

Please make sure your own home is not polluting your local river. Find out more at

ZSL are active members of the Regional Misconnections Group and work in partnership with organisations across the region to help tackle this damaging problem for London’s rivers.

A Guide to Running an Outfall Safari

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Since 2016, Outfall Safaris have taken place on over 250km of river in Greater London and the approach has been adopted by other environmental NGOs across the UK. To support the spread of the Outfall Safari method and drive improvement in urban water quality across the country, ZSL and The Rivers Trust have created the Outfall Safari guide and package of resources to help environmental NGOs and water companies’ setup their own Outfall Safari projects.

Read the guide first to understand how the methodology works and use the resources to help with the technical aspects of setting up and running the Outfall Safari.

We would really value hearing from those that have used the guide and run their own Outfall Safaris. Please contact us at with your feedback, ideas and any general questions that you may have. 


Urban Diffuse Pollution

The impacts from pollutants washed into rivers from roads and other hard surfaces are very complex and poorly understood.  The effects on the receiving waterbodies can be both acute and chronic. Acute impacts occur most often during summer storms after prolonged periods of dry weather, when river levels are low. Materials that have built up on the roads are washed into rivers in one quick ‘first flush’. High pollution loadings arriving very rapidly can lead to the swift depletion of oxygen in the receiving river, which can kill fish in large numbers. There were a number of high-profile damaging ‘first flush’ events during recent summers and climate change is set to increase their frequency. Bound up with the washed off materials are over 600 different chemicals that can exhibit a range of chronic ecological impacts.

In 2018 a group of organisations including Thames21, Middlesex University, South East Rivers Trust (SERT), The Greater London Authority (GLA), the Zoological Society of London (ZSL), The Environment Agency (EA) Transport for London (TfL) and the London Drainage Engineers  Group (LoDEG) were convened as a steering group to guide a programme of work on the topic of road runoff pollution and its impacts on rivers in London. The aim of the group is to position London as a global leader in restoring urban rivers through addressing one of the major pollution sources – road runoff. 
The first task completed by this group was to create a Road Runoff Pollution Risk Map for London which can be viewed here

Resolving the issue of road runoff pollution is complex and will involve novel solutions, policy changes and significant investment. Controlling pollution at source, before it disperses into the wider environment, must be the priority but nature base solutions, such as constructed wetlands, have a role to play in process pollutants in urban environments. In addition to their beneficial effects on water quality, constructed wetlands also bring other benefits including:

  • reduced risk of flooding 
  • reducing the load of contaminated sediments and damaging high flows that are typically found in urban rivers.
  • increased wildlife habitat
  • greater access to nature and opportunities for health and wellbeing benefits of wild spaces for surrounding communities

There is an urgent need to reframe how we manage surface water in London and integrate more constructed wetlands into London’s green infrastructure. The London Borough of Enfield has for some years been leading the way in this. To support the development of more constructed wetlands in London we have worked with them to develop this GLA funded Urban Wetland Design Guide.

We are interested to hearing feedback from those that use this guide so please do get in touch with any comments or suggestions.

Citizen Crane

The Citizen Crane project is a major citizen science initiative on the River Crane in West London. The project is led by ZSL, Friends of River Crane Environment, Frog Environmental with support and guidance from the Environment Agency, Thames Water and The Crane Valley Partnership

All the project reports can be viewed at:

Project information

People involved

Joe Pecorelli and Phoebe Shaw Stewart


  • Environment Agency
  • Frog Environmental
  • Friends of Ickenham Marshes
  • Friends of River Crane Environment
  • Friends of Yeading Brook
  • Greater London Authority
  • Harrow Nature Conservation Forum
  • Kingston University
  • London Wildlife Trust
  • The Riverfly Partnership
  • South East Rivers Trust
  • Thames21
  • Thames Anglers Conservancy
  • Thames Water
  • Transport for London
  • Friends of the River Roding
  • Vision RCL
  • Middlesex University

Kindly funded by:

  • City Bridge Trust
  • Thames Water
  • Greater London Authority
  • Environment Agency

If you would like any of the reports published by ZSL's London's Rivers Team, then please contact us at