Project started
1 March 2014
Project status

London's rivers are a vital habitat for wildlife and a great resource for people, yet they are degraded by poor habitat and pollution. 

Why are we improving London’s rivers?

Urban rivers can provide important opportunities to restore nature to cities. The upside of years of neglect and modification, including the burial of many streams and rivers, is that the opportunities to restore from such a low baseline are considerable. In addition, they are often lined by semi-connected open spaces that, with strategic planning, can be linked as a network of interconnected wildlife sites. Another significant reason to focus on freshwater ecosystem recovery is that freshwater systems, compared to other systems, are disproportionately biologically rich. The 0.8% of our planet that is covered in freshwater is home to more than 10% of all known animal species.

In London, ZSL works with multiple partners to restore rivers. Since 2000 approximately 39 km of river, 6% of the total length of rivers in London, has been restored but we need to do more and faster. The evidence is clear, when rivers are restored wildlife returns. In addition to benefiting wildlife, restoring rivers helps improve water quality, makes the city more resilient to the effects of climate change and the threat of flooding, and supports the well-being of local people. 

  • More than 10% of all known animal species can be found
    in the 0.8% of our planet that is covered in freshwater.
  • What is ZSL doing?

    • Evidence and community science
    • Restoring rivers and wetlands
    • Policy and legislation

    Evidence and Community science

    River Citizen Science Network and annual Forum for London 

    In this age of environmental crisis, we need a range of data and evidence-collection methods to underpin environmental decision-making and to massively scale up our action for positive change. Well-designed citizen science can be a cost-effective and high-impact way of gathering broad and detailed information and can build social capital and connect people to nature.  

    The River Citizen Science Network, chaired by ZSL, is an informal network for practitioners working together to foster greater collaboration between communities, Environment Agency, Thames Water, NGOs and other river catchment stakeholders in Greater London, identify and address thematic and spatial, data and reporting gaps that can be addressed by citizen science.  

    ZSL also hosts an annual Citizen Science Forum for all those that participate in citizen science projects on London's rivers. The forum provides an opportunity to thank Citizen Scientists and show how the data they are collecting is being used to improve London' rivers. It also enables increased collaboration between NGOs, statutory agencies, policy makers and businesses in London as well as allowing organisations to highlight future opportunities for volunteering. See below for more details on the citizen science projects you can get involved with. 


    The Riverfly Monitoring Initiative

    ZSL are on the Riverfly Partnership’s Advisory Board. The Riverfly Partnership developed and run the Riverfly Monitoring Initiative (RMI), 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 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.

    If you are already involved in Riverfly monitoring and are looking to record data onto the cartographer map – see this guide or sign into cartographer here. To get involved in Riverfly Monitoring, see How to Volunteer.

    Evidencing sources of pollution: 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. Until recently, there has been no systematic surveying of outfalls in urban rivers to identify pollution and notify the relevant authorities. The Outfall Safari Project was developed by ZSL in 2016 in partnership with Thames Water, the Environment Agency (EA), fellow NGO’s and communities in Greater London. It is a citizen science method devised to address this evidence gathering and reporting gap.

    Volunteers attend a training session to learn how to identify outfalls, how to rank the extent of pollution and how to report severely polluting outfalls to Thames Water. Volunteers are then allocated a section of the riverbank to survey. Volunteers use an app to record the location and condition of the outfalls and once surveys have been completed, staff fill in any inaccessible areas by completing in channel surveys. The results of all surveys are then sent to Thames Water, who use the data to identify the sources of pollution from the outfalls and prevent further pollution entering the rivers from misconnections. Every year, the Outfall Safari program surveys four rivers within London and has recently expanded to survey urban waterbodies beyond Greater London, within the wider Thames Water operational boundary. For information on when we carry out surveys and how to get involved, please see How to Volunteer

    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.

    Read our report on tackling pollution in London rivers

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

    A guide to running an outfall safari

    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 these 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.  

    The Citizen Crane Project

    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 here

    Catchment Systems Thinking Co-operative (CaSTCo)

    CaSTCo is an Ofwat funded project led by the Rivers Trust and United Utilities which aims to change how citizen science contributes to evidence based river catchment management. ZSL helped to develop CaSTCo and sit on the steering group for the project. As part of CaSTCo, ZSL are also carrying out a method audit on citizen science freshwater fish monitoring methods in order that guidance can be produced to enable increased standardisation of methods and consistent monitoring within citizen science freshwater monitoring.


    Restoring Rivers

    ZSL are members of the River Partnerships in London Working Group. We are working collaboratively to restore river habitats in London. Read more about our river and wetland restoration projects below.

    Smarter Water Catchments

    The Crane catchment has been selected as a pilot for Thames Water’s Smarter Water Catchments (SWC) initiative which aims to deliver a step change in holistic catchment management as a collaborative way of addressing the challenges and opportunities of rivers and their associated open spaces. The Crane is the first urban river system in the Thames Region to be considered in this way. The Crane Smarter Water Catchments Plan has identified the following five key themes to be addressed:  

    • Promote public awareness, access, and participation,  
    • improve water quality,  
    • enhance flood resilience,
    • enhance biodiversity – wildlife and their habitats,
    • improve geomorphology – the river form.

    ZSL are Theme Leads for Water Quality and Biodiversity and have fed into the State of the Crane report, which provides an overview of the progress made after the first two years of the Smarter Water Catchments initiative.

    Restoring populations of key species

    Water Vole - ecosystem engineers

    Water voles are ecosystem engineers, their population dynamics, feeding and burrowing behaviour can influence their local environment. Feeding on the roots and shoots, water voles can prevent a single plant species from becoming dominant and can help with seed dispersal. Their burrowing can also influence the soil, impacting the availability of nutrients for plant growth. Studies suggest that with the declines of water voles, plant communities become less diverse. At the base of the food chain, water voles are also an important food source for many of our native predators that exist along rivers and wetlands. Their absence results in an ecosystem that is less stable and an overall biodiversity loss for our rivers and wetlands. ZSL is working with the People’s Trust for Endangered Species, Greenspace Information for Greater London and the London Wildlife Trust as part of the London Water Vole Recovery Programme, which aims to restore water voles to the capital, an area where they once thrived.  

    Find out more about this important species and get involved in water vole conservation here

    European Eel - eel passes and connectivity

    European eels once thrived in London’s rivers but the number of young reaching our rivers and making it into adulthood has dropped dramatically since the 1980s; the species is now classified as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. As well as working with citizen scientists to monitor eel recruitment into the Thames each year, ZSL works to reduce the threats facing eels. For example, by reducing barriers to migration by installing eel passes so that eels can move upstream over weirs.  

    Find out more about the important eel conservation work carried out by ZSL and get involved here. 

    Wetland Creation

    Constructed wetlands are specifically designed features installed in the landscape that use naturally occurring physical, ecological and chemical processes to sustainably intercept and treat polluted water, slow flows to help reduce flood risk and help to improve the ecological health of surface water systems.

    You can find our guidance on the design of Urban Wetlands, produced in partnership with London Borough of Enfield and The Greater London Authority in this handy guide. This guide provides practical advice to inform the design and maintenance of constructed wetlands for treating water pollution and was produced with the support of a wider partnership led programme of work in London to address the issue of waterborne pollutants from roads.  

    Although the benefits of urban constructed wetland systems are well recognised with numerous wetland creation projects being carried out across London, relatively little information is available for comparison of monitoring data to other urban (and more specifically London) wetlands systems.  

    As a result, and following the creation of a new wetland at Headstone Manor Park, ZSL collaborated with local volunteers to assess and monitor the water quality and biodiversity impact of the wetland. The Evidencing the Impact of Constructed Wetlands: Headstone Manor Park Report was created as part of the Thames Water’s Smarter Water Catchments initiative and following on from the recommendations of this report, a pilot project is underway to develop a citizen science wetland invertebrates sampling system. 

    Water vole poking out from burrow along a river bank

    Policy and Legislation

    ZSL is a member of the Wildlife and Countryside Link Blueprint for Water Group helping shape policy that impacts freshwater environments across the UK.


    • Citizen Zoo
    • Crane Valley Partnership  
    • Environment Agency
    • Frog Environmental
    • Friends of River Crane Environment
    • Greater London Authority
    • Green Space Information for Greater London  
    • Let’s Go Outside and Learn
    • London Wildlife Trust
    • London Borough of Harrow  
    • London Borough of Hillingdon
    • London Borough of Richmond  
    • The Riverfly Partnership
    • People Trust for Endangered Species  
    • South East Rivers Trust
    • Thames21
    • Thames Water

    Kindly funded by:

    • Esme Fairbairn Foundation  
    • 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

    Hear from ZSL volunteers

    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