It affects the whole food chain, from aquatic plants, invertebrates and fish, through to birds such as grey heron and great-crested grebe and mammals such as water shrew and seals.

What causes pollution?

Pollution is usually associated with chemicals and high levels of nutrients, which may either be discharged directly into water bodies, either deliberately or accidentally. In London, the pollution is a cocktail of:

• Leakages from overburdened sewage systems
• Poor plumbing from domestic and business properties
• Cleaning agents, food (e.g. ‘fatbergs’), beauty products, drugs, paints, oils, metals, and other chemicals
• Surface water run-off from roads, rail, car-parks, airports and buildings which contains things like brake-dust, tyre particulates, vehicular exhaust pollutants, anti-freezing agents, or pesticides
• Agricultural run-off which can include fertilisers and pesticides
• Litter

These are just a few of the types of pollutants that end up in our rivers.

How does pollution impact wildlife?

Wildlife is adversely affected by water pollution in a number of ways:

Direct poisoning

Wildlife can be directly poisoned through toxic levels of certain chemicals. These become more acute if water levels and/or oxygen levels are low.

In the 80s, DDT in the food-chain caused a huge decline in peregrine falcon numbers as it weakened their egg-shells so that in effect they became infertile. DDT usage was banned in the UK in 1986 - but a similar scenario could play out in the food chain of rivers if water pollution isn’t addressed. 

Eutrophication

A high level of nitrates and phosphates can cause eutrophication - where there is a rapid increase in plant growth, particularly algae. Algae uses up oxygen, turns the water green and blocks out light. This in turn suffocates aquatic life. 

Suffocation

Absorbable dissolved oxygen in water is essential for wildlife to survive. When raw sewage enters a river system it is broken down by bacteria, creating ammonia (thereby increasing alkalinity), which uses up a great deal of oxygen. 

What is the waterbody quality in London?

The Thames Basin River Management Plan (2022) defines the London catchment as having 47 water bodies (made up of rivers, canals and lakes). The ecological status of the 47 water bodies is:

High = 0

Good = 3

Moderate = 33

Poor = 9

Bad = 2

The below chart shows the issues preventing waters reaching good status and the sectors identified as contributing to them. The numbers in the table are individual counts of the reasons for not achieving Good status.

What London Wildlife Trust is doing about it

Nature-based solutions

We have a long history of working to enhance the quality of London’s waterbodies. Using nature-based solutions, we have focused on securing ecological benefits with many also being designed to reduce or capture pollutant inflow. Some of the projects we have worked on include:

• Creating floating reedbeds
• Creating backwaters
• Restoring meanders and natural river profiles
• Desilting and replanting ponds
• Removing invasive species

Nature reserve management

As well as this, we manage a number of nature reserves where aquatic habitat conservation and restoration are key elements. These include:

• Denham Lock Wood (wet woodland and Frays River)
• Woodberry Wetlands (primarily the reedbeds)
• Spencer Road Wetlands (reedbeds)
• Wilderness Island (ponds and the River Wandle)
• Walthamstow Wetlands (reservoirs that benefit waterfowl)
• Bramley Bank (pond)
• Park Road Pond
• Gunnersbury Triangle (pond)
• Uxbridge Grove (two ponds)
• Oak Hill Wood (deculverting a tributary of the Pymmes Brook)
• Frays Island & Mabey’s Meadow (banksides)
• Frays Farm Meadows (Frays River and ditches)
• Crane Park Island (reedbed and ditches)
• Gutteridge Wood (Yeading Brook)
• Ten Acre Wood (Yeading Brook and pond)
• Yeading Brook Meadows

Advocacy and influencing 

We work alongside other groups to help shape plans that will impact London’s waterways and waterbodies. These include:

Tideway - supporting the construction of Tideway, to help reduce the 13.2 million tonnes of sewage being discharged into the Thames downstream from Fulham. 

Catchment groups -  as part of the River Partnerships in London, we co-host the Thamesmead & Marsh Dykes Catchment Improvement Group and are members of other catchment groups in London,  helping to shape catchment plans for the Thames and its tributaries, secure resources for projects and advocate for policy changes.

How you can help 

One of the best ways you can help is by joining us as a member and helping us continue the work we do to protect London’s rivers and waterways. 

You can make a real difference. Your monthly gift will:

• Challenge actions and developments that threaten wildlife
• Care for more than 36 nature reserves across London
• Conserve rare species and nature in the capital

Join us and help us protect London’s rivers