London's Rivers

The Riverfly Monitoring Initiative (RMI) is a scheme created by The Riverfly Partnership, a dynamic network of organisations working together to protect river habitats for wildlife and to improve water quality. 

The RMI scheme is a UK wide citizen science scheme that looks at the diversity and abundance of 8 key pollution-sensitive aquatic invertebrates in the river. This enables us to assess water quality, detect pollution events and learn about long-term trends of river health. To do this, volunteers are trained in how to conduct kick-samples in the river, taxa identification and how to record data. Volunteers then conduct monthly surveys at fixed RMI sites. 

ZSL are an active board member of The Riverfly Partnership and 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.

If you are already involved in Riverfly monitoring and need 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.

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 the need for gathering evidence and reporting gaps.

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

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

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 a package of resources to help environmental NGOs and water companies setup their own Outfall Safari projects. The guide provides an understanding of how the methodology works and the resources help with the technical aspects of setting up and running the Outfall Safari: 

Tackling Pollution in Urban Rivers: A Guide to Running an Outfall Safari

• Volunteer training presentation template, Volunteer handout template and Outfall Safari report template
• Alfreton Brook case study
• ArcGIS online resources – access to these can be requested via the CaBA website

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

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 and 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

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 helping to roll out the Outfall Safari method more widely - more info can be found on the CaSTCo website here.

The Crane catchment has been selected as a pilot for Thames Water’s Smarter Water Catchments (SWC) initiative, which aims to deliver a change towards 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.

Water Vole - ecosystem engineers

Water voles once thrived across London's waterways but due to non-native American mink, and habitat loss they are now endangered in Great Britain. Water voles are important for rivers as they are ecosystem engineers. This is because 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 help with seed dispersal. Their burrowing can also influence the soil, impacting the availability of nutrients for plant growth. Studies suggest that with the population decline of water voles, plant communities are becoming 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 a less stable ecosystem resulting in 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..  

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

European Eel - eel passes and connectivity

European eels also once thrived in London’s rivers but the number of young eels reaching our rivers and making it into adulthood has dropped significantly since the 1980s, resulting in the species now being 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. 

Constructed wetlands are increasingly being used as Nature Based Solutions, specifically designed within a landscape to use naturally occurring physical, ecological and chemical processes to intercept and treat polluted water. They also slow water flows to reduce flood risk, improve water quality, and provide important habitats for wildlife. In addition to these ecological functions, wetlands enhance urban green spaces, supporting biodiversity and improving wellbeing for local communities.

However, the benefits of wetlands depend on how well they are designed, maintained, and managed. Poorly designed or overloaded wetlands can quickly lose their biodiversity value or fail to process pollutants effectively. To help practitioners maximise benefits, ZSL collaborated with the London Borough of Enfield and the Greater London Authority to produce the Urban Wetlands Design Guide. This provides practical advice on creating and managing urban wetlands for pollution treatment, flood resilience, and biodiversity gain.

Why is monitoring important?

Monitoring is essential to ensure wetlands function as intended over the long term. Ecological monitoring, particularly of aquatic invertebrates, provides insights into how well wetlands are improving water quality and supporting biodiversity. Traditionally, methods such as the Riverfly Partnership’s Riverfly Monitoring Initiative have been used to track river health, but until recently no equivalent approach existed for urban constructed wetlands.

To fill this gap, supported by the Greater London Authority, ZSL developed and trialled the Constructed Wetland Monitoring Method (CWMM) in partnership with volunteers and community groups. This citizen science tool enables routine monitoring of wetland invertebrates at both the inlet and outlet of a system, providing an indication of whether water quality is improving across the wetland.

As an example, our work at Headstone Manor Park wetlands investigated the ecological performance of a newly created wetland, which illustrated both the importance of monitoring and the challenges wetlands face. Following the creation of the site, a major investigation revealed that extreme summer temperatures, drought, and high pollution loads caused a temporary system failure. This evidence was published in the report Trialling the Constructed Wetlands Monitoring Method with Community Scientists, highlighting the importance of ongoing assessment and the value of involving local volunteers in monitoring.

Building on these findings, ZSL worked with partners including Thames21, Citizen Crane and local Friends groups to refine the methods further and create a standardised approach that allows citizen scientists to monitor biodiversity and invertebrate communities in constructed wetlands. The led to the production of the Wetland Monitoring Method, a practical guide that provides tools and protocols for systematic community-based monitoring.

You can also watch our short film introducing the method here: Constructed Wetland Monitoring – ZSL.