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join an outfall safariFancy going on safari with the Zoological Society of London? Free, with no tedious long flights to get there?

Well, ZSL's Marine and Freshwater division is offering you the opportunity this March and April. You're very unlikely to come across any lions, tigers or crocodiles, and some of the things you do come across might not be very appealing, but you'll be helping clean up our local streams and rivers and contributing to healing north London's natural environment.

The expeditions in question are called "outfall safaris" and Instead of looking out for wild animals you'll be walking riverside paths, looking out for pollution entering the river Lea and its tributaries (such as the Pymmes Brook and Salmons Brook) via "outfalls", that is, points where water from drains enters the rivers. The water in the drains should be mostly rainwater and relatively clean, but unfortunately some houses and flats have been incorrectly plumbed and are sending foul wastewater into the rainwater system and from there into the Lea and ultimately the Thames.

What exactly is an 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. Mis-connections between the two drainage systems, often caused by inexpert plumbing, result 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 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
  • Geo-locate 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.


To take part you need to attend a training day at Walthamstow Wetlands on 23rd March. You're requested not to attend unless you're actually intending to join the "safaris".

See below for more details of the training day and what the outfall safaris involve.

Please help find sources of pollution in the lower Lea and tributaries by joining an outfall safari

Pollution can find its way into urban rivers via surface water outfalls (drains) as a result of misconnected plumbing. We are looking for volunteers to help conduct Outfall Safari surveys on the lower Lea and tributaries. This involves bankside surveys of stretches of the river to map and record the impact of outfalls.

The surveys will take place during: March—April 2023

As a volunteer, you can choose which stretch of the river and at what time to conduct the survey, within the survey period. The survey will be conducted from the riverside path, in areas that are accessible and where the river is easily visible. Training will be provided by ZSL.

The training session will take place at Walthamstow Wetlands, London Wildlife Trust, 2 Forest Road N17 9NH, on Thursday 23rd March at 10:30-12:30.

Register at, For more information please email:

Once registered, more information will be sent to you about how to join the training.

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