Freshwater Habitats Trust statement on the impact of sewage pollution on freshwater habitats and species
1st November 2024
Sewage pollution is a major pressure on the UK’s freshwaters, and we applaud the work of eNGOs and grassroots groups in raising the profile of this vital issue. Although upgrades to sewage infrastructure led to some ecological recovery through the 1990s and early 2000s, this progress has arguably now stalled, and the UK’s freshwater biodiversity is still widely degraded by treated and untreated wastewater. Freshwater Habitats Trust staff are researching the impacts of this wastewater on our highest quality freshwaters, and developing new approaches to reducing these impacts.
Currently, water industry investment is overwhelmingly focused on upgrades to sewage infrastructure, mostly affecting the lower reaches of rivers. Sewage is just one of the many problems affecting our freshwaters, and simply cleaning up sewage in larger rivers will not automatically deliver the biodiversity improvements which we all want to see.
A new approach is required, which harnesses water sector investment to address the multiple pressures on freshwaters across catchments and from source-to-sea. This approach would direct much more investment towards upper reaches, where we can ‘start at the top and work down’, upgrading small sewage treatment works and targeting catchment measures towards the much smaller catchments of headwater streams, where changes to agricultural practices over small areas of land can deliver much bigger biodiversity gains. Simultaneously, clean water would be added to the landscape via the creation of ponds and wetlands. Taking this new approach, we could halt the decline of sensitive freshwater species, and create growing networks of unpolluted freshwater habitats.
The water industry will spend billions on environmental improvements during Asset Management Period 8 (AMP8: 2025-2030). This investment is very welcome, but as currently conceived will deliver only modest improvements, across a relatively short length of the river network. This is because investment is too narrowly focused on sewage infrastructure, and smaller waters are deprioritised.
The Environment Act instated a target to reduce phosphorus from treated wastewater by 80% by 2038. This target is exclusively focused on gross reduction in water pollution (i.e. tonnes of phosphorus), irrespective of where that pollution is entering the environment. Because reducing the total volume of sewage entering rivers is cheapest at large sewage treatment works, investment is resultingly focused on large sewage treatment works, which mostly discharge into larger rivers.
A number of lines of evidence, summarised below, show that this approach is an ineffective way of delivering environmental improvements.
- Because of their large catchments, large rivers are generally impacted by many different sources of pollution, from multiple sectors. It is therefore very difficult to ‘clean up’ large rivers, and deliver ecological improvements. By contrast, smaller streams have correspondingly smaller catchments, so are affected by fewer upstream sources of pollution. As a result, it is easier to deliver environmental improvements in smaller streams.
- A recent Europe-wide study demonstrated that, in small (1st-3rd order) streams, single small sewage treatment works were often responsible for preventing waterbodies from achieving Good/High ecological status under the Water Framework Directive. It follows that, by upgrading these small works, the ecological status of these waterbodies could be significantly improved.
- 1st, 2nd and 3rd order ‘headwater’ streams make up more than 70% of the river network, and are vital for freshwater biodiversity. Deprioritising headwaters for investment means that only a minority of our running waters can be improved.
Redirecting investment so that small sewage treatment works in small rivers are more widely upgraded would be a good first step. However, investment in sewage infrastructure can only ever be part of the solution, because sewage pollution is only ever part of the problem. Freshwaters are also heavily impacted by pollution from intensive agriculture, road runoff and industry.
Catchment-based measures – like agricultural deintensification – can tackle these sources of pollution, and reduce the total pollutant load impacting a waterbody. However, as with investments to sewage infrastructure, catchment-based measures can only be effective where other sources of upstream pollution are addressed. Catchment measures are therefore most effectively targeted at upper catchments, where there are fewer upstream sources of pollution to contend with.
We argue that the most effective approach to tackling pollution would see the water sector starting at the top and working down, using a mixture of upgrades to sewage treatment (including nature-based solutions) and catchment measures as appropriate.
In time, the efficacy of water sector environmental investment could be significantly increased by recognising freshwaters as interconnected networks, existing across landscapes in multiple habitat types. In catchments where main channels are heavily polluted, it could be more cost-effective to add new clean water. This could be achieved through the creation of small standing waters in sub-catchments which are free from pollution. This would improve the water environment at a catchment-scale, and create refuges for the pollution-sensitive plants and animals which have disappeared from our larger lakes and rivers. Over time, as larger waters are restored, pollution-sensitive species would be able to spread out from these refuges to recolonise the wider catchment.
Pollution is just one of the many growing threats to the UK’s freshwater ecosystems. We’ve proposed a Reset for Water – a new approach to management of the water environment which would enable recovery of freshwater biodiversity at landscape-scale. This focuses on protecting the best freshwater habitats, and building out from these to create new, clean, freshwaters.