Our everyday lives are filled with chemicals. From the cleaning products we use, to the medicines we take and the food we eat.
photograph of dead fish in polluted water
Chemical use provides many benefits. However, when we’re finished with chemicals, they don’t just disappear. Pesticides, pharmaceuticals and plasticisers (chemicals used to soften plastic) leak into the environment, entering our air, soil and water, and causing unwanted effects in addition to the desired ones.
photograph of dead fish in polluted water
The sheer number of different chemicals, and the complicated way they interact with each other, means we cannot possibly understand the real-world impacts. But we do know that chemicals persist in the environment for months or even years. They contaminate nearby habitats and cause significant harm to wildlife – on land, in the sea and in freshwater.
photograph of white tailed bumblebee on flower
photograph of humpback whale surfacing
photograph of leaping Atlantic salmon
We already know that many terrestrial and freshwater species are in decline and at risk of extinction. In 2021, scientists concluded that we had crossed the planetary boundary for chemical pollution, meaning that levels of chemicals in the environment are no longer safe for humanity.
photograph of a water vole on a small rocky river island
Chemicals are just one of a number of pollutants threatening our freshwater ecosystems.
Sewage, plastic, excess nutrients and waste from farmland all contribute to the dire state of our rivers.
photograph of grey heron fishing along a river, near blue plastic bag causing potential problems for wildlife
Environment Agency data from 2020 showed that all English rivers failed to meet overall quality tests for pollution. Not a single river achieved good chemical status, and only 14% of rivers in England achieved good ecological status.
photograph of degraded river bed
Our findings
Aquatic invertebrates live in rivers for most, if not all, of their lives - sometimes for years. Over this time they are directly exposed to the conditions of the water, and often need good water quality to reach maturity.
Finding species like these indicates that overall water quality is likely to have been good for an extended period. Therefore using
invertebrates provides insight into river health over a broad period of time.
close up photograph of stonefly on river bed
WildFish have published their latest Riverfly Census results – a survey covering 12 English rivers. Samples were collected and analysed to look at invertebrate biodiversity and the pressures impacting freshwater habitats.
Exposure to pesticides, herbicides and other chemicals changes invertebrate community composition. The Species at Risk metric, or SPEAR, looks at this composition and provides a stress score based on the invertebrates present. Looking at these data has allowed us to determine if, and how, chemicals are impacting aquatic wildlife, and whether the problem is getting better or worse.
photograph of caddisfly larvae
We looked at the 2021 SPEAR scores and compared them to results from previous years. The data showed that there was not much difference in spring between the different years, but the autumn results told a different story. The proportion of sites where the invertebrate community indicated Poor or Bad on the chemical stress scale was considerably greater in autumn 2021, compared to autumn results from 2015, 2016 and 2017.
These results show that invertebrate communities are more stressed from chemicals now than they were in previous years. This strongly suggests the problem is getting worse. But, the level of chemical stress on its own doesn’t tell us what is happening to biodiversity.
EPT stands for Ephemeroptera, Plecoptera and Trichoptera. These are orders of aquatic invertebrates better known as mayflies, stoneflies and caddisflies. As a general rule, 20 or more EPT species in a sample indicates high water quality. A variety of EPT species, rather than just high abundances of one or two species, is what we're looking for in a healthy system.
photograph of adult common mayfly clinging to bankside vegetation
Not only are rivers suffering greater chemical stress, the diversity of key invertebrate species also appears to be decreasing.
Why do riverflies matter?
Most freshwater animals are invertebrates. In the UK, over 4,100 invertebrate species spend at least part of their lifecycle in freshwater.
photograph of an adult mayfly arising from the water
Aquatic invertebrates play a vital role in maintaining clean water, recycling organic matter and providing a food source for fish, birds and mammals. Without them, the food web would collapse.
photograph of adult grey heron standing on fallen tree in river
photograph of European otter foraging around small river island
More than 280 species of mayflies, caddisflies and stoneflies are present in Britain.
close up photograph of adult scarce grey flag caddisfly
Twenty-four species are classified as threatened, and a further four species considered extinct in the UK. We also have several species which are endemic, found nowhere else in the world.
photograph of adult northern February red stonefly
River Avon case study
WildFish manage a project called SmartRivers, the citizen science ‘sister’ of the Riverfly Census.
SmartRivers enables volunteer hubs, supported by a certified training scheme, to sample and analyse invertebrates to a near-professional standard and learn more about the state of our rivers.
photograph of SmartRivers volunteers studying together in a river
On the River Avon, Wiltshire Fisheries Association have continued the Census monitoring via our SmartRivers programme. They now survey the original Census sites, plus six more.
The data show a dramatic fall in numbers of invertebrates within the last five years, and concerning SPEAR signatures.
The Avon catchment consists mainly of rare chalk streams and is a Site of Special Scientific Interest (SSSI) and Special Area of Conservation (SAC).
In a very short time, it has fallen from being one of the highest quality UK rivers, with abundant river life, to being defined by the Environment Agency as ‘moderate’, with a rapidly declining invertebrate population.
The Avon catchment probably holds a greater variety of indigenous fish species than any other river in the British Isles, including the iconic - and declining - Atlantic salmon.
photograph of leaping Atlantic salmon
What can be done?
Rivers and the wildlife that they support are facing a multitude of threats – a death by a thousand cuts.
As 40% of pollution in rivers is agricultural, one of the key solutions is to tackle this. This involves:
better support for farmers to reduce their reliance on pesticides and artificial fertilisers. Many farmers are turning to nature to help them do this, as part of a regenerative agricultural system;
enforcement of existing farming regulations designed to protect rivers from agricultural pollution.
photograph of Friesian cattle cooling themselves in a stream
Recommendations for Government
Ensure that the new Environmental Land Management Schemes support farmers to reduce their reliance on pesticides and artificial fertilisers
Invest in non-chemical alternatives including research and advice
Maintain a precautionary approach to chemical approvals post-Brexit
Properly commit to and resource a comprehensive river monitoring network and enforcement of existing regulations
Improve gaps in the risk assessment for chemicals before they are approved, and carry out assessments on chemicals already in use to better understand the real-world impacts
Conclusion
Evidence is clear that our freshwater habitats are suffering. Stopping pollution at source is better than removing it once it’s there – in other words, prevention is better than cure.
The cost of cleaning up our rivers is eye-watering. Costs arising from the contamination of drinking water with pesticides alone in the UK, have previously been calculated at £120 million per year.
But we are also in a biodiversity crisis, and we must urgently reverse this. The future depends on it.
photograph of rushing water at Naddle Beck, RSPB Haweswater Nature Reserve
