River otter sat on grass

5 animals impacted by sewage

Water companies are currently allowed to pour tonnes of sewage into our waters every day. Zoologist and campaigner Sienna Somers looks at the animals suffering because of sewage.
  Published:  15 May 2024    |      3 minute read

Last year I had the joy of accompanying a group of 10-year-olds to do river dipping on a chalk stream. They were there to learn more about our rivers, the species that call it home and the threats they face. I won’t forget the look of pure delight on their faces as they unearthed these ”mini-beasts” (aka river invertebrates) from the bottom of the stream bed and then meticulously sorted and identified. One kid even screamed in delight upon finding a leech.

But the mood quickly changed when I told them about the dangers facing our rivers. Sewage pollution transforms rivers into hostile environments, endangering the existence of many iconic and important species and precious ecosystems.

Here are just 5 species that are suffering because of our sewage:


Mayflies spend much of their life on river beds, before emerging in the summer to perform mesmerising dances over our rivers and lakes. At the bottom of the freshwater food chain, they’re often used as a signal of river health. A drop in their numbers can have ripple effects up the food chain as they’re the food source for many fish and birds. They rely on clean waters to live, and the influx of nutrients from sewage pollution causes an explosion of algae, preventing them from feeding and killing off their eggs.


Dipper bird perches on a wet mossy rock with a river in the background
Dipper bird by a river
Credit: Vic Thornley/ 500px via Getty Images

Meet the dipper, our canary in the coal mine for polluted rivers. Uniquely adapted to swim and dive in rivers to feed, dippers rely on a steady supply of invertebrates, such as mayflies, and fish in the river. They’re one of the few birds that indicate water quality, disappearing from polluted rivers and returning when clean.


With their slick coats and big brown eyes, the Eurasian otter is surely one of our most well-loved river creatures. But as top predators, they're particularly vulnerable to chemicals that build up along the food chain. Recent research shows that otters across Britain now have high levels of toxic "forever" chemicals in their bodies, and that they likely ingested these chemicals from sewage pollution. While we don’t know exactly what impact these chemicals are having on these beautiful creatures yet, there’s been a drop in otter sightings, particularly in Wales where sites with signs of otters have dropped by 22% since 2010. We’ve also witnessed dramatic drops in eel numbers, otters’ favourite food.

Atlantic salmon

Atlantic salmon jumps out of the air to swim upstream against a waterfall
Atlantic salmon swims upstream
Credit: Gregg Parsons via Getty Images

Did you know that Salmon found in our chalk streams are genetically unique, classing them as a separate sub-species? Salmon can migrate over thousands of miles from the icy waters of the North Atlantic to the rivers of the UK to release their eggs (spawn). But the number of salmon who’ve returned from their migration to our rivers has plummeted in recent years, even in our famous chalk streams. Pollution is making it harder for salmon to spawn in our rivers and young salmon who return to the sea are likely to be smaller and less likely to survive. The situation is so bad that the Environment Agency now warns this iconic species could be lost from our rivers forever in a matter of decades.


Orange crab sits on a rock
Crab on a rock in Essex, UK
Credit: Geraint Rowland Photography via Getty Images

It’s not just our river-dwelling species that are impacted by sewage pollution. Our marine animals are suffering too. In a recent study, every species tested in the English Channel was found to have a "cocktail" of pollutants in their bodies from antidepressants, contraceptive pills, as well as illegal drugs such as cocaine and methamphetamine, originating from sewage discharging into our rivers and seas. In crabs and other crustaceans, this has been shown to alter their behaviour, their growth and even their reproduction. It's a sobering reminder that what we put in our bodies and our drains impacts marine creatures in ways we are only just understanding.

All these species, and many more, rely on clean, healthy waters. We’re campaigning for our right to a healthy environment to be enshrined into law, and for companies that disregard nature and people to be held accountable. This would mean water companies would have a legal duty to contribute to a healthy environment and prevent our government from scrapping environmental protections in the future.