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. Help us health-check our rivers as part of the London's Rivers project.

Volunteer to healthcheck London's rivers

Why we are improving London’s rivers

As more and more people around the world move to cities it is essential that we learn how to accommodate wildlife in 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 in the capital. 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 the most widely adopted aquatic citizen science scheme in the UK and was developed by the Riverfly Partnership and is funded and endorsed nationally by the Environment Agency. It is for detecting and reporting pollution events, gathering long term river health data and aligning the efforts of trained volunteers and the Environment Agency in improving rivers across the UK.

As the London Riverfly Monitoring Hub, ZSL supports the development of RMIs on new rivers in London and along with our partners support the six RMI schemes already up and running.  These are on the Rivers Crane, Wandle, Hogsmill, Pinn, Ravensbourne and Cray

RMI sampling is based on long established principles of water quality testing that uses key invertebrate species as indictors of the ecological health of rivers. The sampling method is learnt in a day and once trained the scheme enables individuals to take responsibility and ownership of their local rivers and to increase the frequency and coverage of monitoring activity.  By monitoring a range of sites on a monthly basis the chances of detecting pollution events are increased and action can be taken early to identify any source of pollution and to resolve the cause.

Volunteers being trained in the RMI sampling method on the River Hogsmill
Volunteers being trained in the RMI sampling method on the River Hogsmill

Volunteers being trained in the RMI sampling method on the River Hogsmill

Misconnections and the Outfall Safari

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

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

Misconnections polluting rivers in London
Misconnections polluting rivers in London

Misconnections polluting rivers in London

Within the Thames Water drainage area, there has until recently been no systematic surveying of outfalls in 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. It has been regarded by the Environment Agency as best practice.

The OS 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

Outfall Safari Guide
Outfall Safari Guide

Since 2016, Outfall Safaris have taken place on over 140km 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. 


Waterborne pollutants from roads

The impacts on rivers of pollutants washed into them from roads and other hard surfaces is a very complex and poorly understood one.  The effects on the receiving waterbodies can be both acute and chronic, long term. Acute impacts are most often witnessed 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.

ZSL has recently embarked on a body of work with its partners to help tackling this serious pollution issue that is threatening London’s aquatic environment. The current phase 1, Road Runoff Pollution Risk Mapping project, funded in by EA, GLA and TfL, and led by Thames21 will for the first time enable the quantification of concentrations of pollutants washed from roads to rivers and identify highest risk zones or hotspots. Phase 2, the essential next step, is to use the hotspots information to identify and prioritize specific transport outfalls and work with stakeholders and communities across London to develop practically scoped out action plans that incorporate best practice pollution interception options to mitigate the impacts of pollutants on rivers.

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

ZSL’s Joe Pecorelli manages the London’s Rivers projects.


  • 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

Kindly funded by:

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