London’s Rivers

Citizen science volunteers

Improving London’s rivers

An intricate network of tributaries flow in to the river Thames in the London region.  ZSL is engaged in a suite of projects harnessing the energy and enthusiasm of local communities to improve the quality of rivers in the capital, helping to create a better environment both for wildlife and for local people. Working together with a number of local grassroots organisations, in close collaboration with the Environment Agency, ZSL are leading on initiatives to monitor water quality, identify sources of pollution and to raise awareness of issues which can impact on river health.  

The state of London’s waterways

The rivers and streams of London 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 a wildlife habitat or as a natural resource for Londoners, and, as such, are in immediate need of our help.

River Monitoring Initiative

The River Monitoring Initiative (RMI) is a methodology developed nationally by the Riverfly Partnership as a means of monitoring water quality.  The technique is based on sampling to establish the presence and abundance of  particular groups of easy to identify invertebrates. The system is a version of a technique used by the Environment Agency, which has been simplified to encourage involvement by citizen science volunteers, enabling 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.

ZSL coordinates and supports the implementation of the RMI in London’s rivers, with the first initiatives starting up on the rivers Crane and Hogsmill in 2014, and a further scheme launching on the Ravensbourne in 2016 in association with Thames 21.

We have published the year two report on the Hogsmill River’s Riverfly Monitoring Initiative (January 2017).

Outfall mapping and pollution detection

In 2016, as part of the Citizen Crane Project partnership, ZSL have launched an exercise to map and assess the impact of all outfalls draining into the River Crane in west London.  A mobile app has been developed which enables volunteers to collect data on a walking survey of the river, recording the locations of all outfalls and assessing the level of any pollution flowing from it.  Results from the surveys will be used to prioritize remediation work by water companies.  This methodology will be scaled up to cover further catchment areas across London, beginning with the River Hogsmill and Dollis’ Brook. 

We have published the report on the Hogsmill River Outfall Safari (November 2016)

Citizen science volunteers being trained in the RMI sampling method on the River Crane


Much of the London region is serviced by two separate drainage systems.  The first of these collects rainwater runoff, from roads and elsewhere, and flows directly into our rivers.  The second collects foul water from building soil pipes and passes through a water treatment works to be cleaned and filtered before it is released into the river system. Misconnections between the two drainage systems, often caused by inexpert plumbing, results in pollution pouring into our rivers  - 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.

Project information

People involved

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


  • Arocha
  • Environment Agency
  • Epsom and Ewell Borough Council
  • Frog Environmental
  • Friends of Ickenham Marshes
  • Friends of River Crane Environment
  • Friends of Yeading Brook
  • Harrow Nature Conservation Forum
  • Kingston University
  • Kingston Biodiversity Network
  • London Wildlife Trust
  • The Lower Mole Project
  • The Riverfly Partnership
  • South East Rivers Trust
  • Thames 21
  • Thames Anglers Conservancy
  • Thames Water

Kindly funded by:

  • City Bridge Trust
  • Crane Valley Partnership
  • Postcode Local Trust
  • Thames Water / Wild Trout Trust (Rivers and Wetlands Community Days)