Green algae bloom at the side of a lake by a wooden pontoon

How to spot water pollution

Almost all the UK's waterways are polluted. Join our call for a new law to punish polluters, and keep safe by learning how to spot pollution in your river.
  Published:  15 May 2024    |      4 minute read

We should be able to swim, paddle or walk alongside clean rivers bursting with fish, otters, kingfishers and many more. But in many places across the UK, that’s far from the reality.

Whether it’s disgusting sewage or invisible microplastics, water pollution is plaguing our rivers and seas. Not only is it harmful to our health, it also wreaks havoc on these precious ecosystems and the species that live in them.

We’re calling for a new environmental law which would grant us the right to a healthy environment and enable us to hold polluters to account.

In the meantime, here are some top tips to help you avoid illness and lobby local leaders to support our cause.

How to spot pollution in rivers

Sights and smells

  • Sewage in the river can look brown or milky grey if it’s been mixed with other wastewater before it reaches the river. Some studies have shown that cloudier water tended to have more sewer bacteria. If you think you can see sewage, you can walk upstream to locate the source coming from a sewage pipe.
  • Sewage litter. An obvious sign of sewage pollution is sewage litter, like personal care or sanitary items.
  • Smells. Sometimes sewage can have an obvious unpleasant smell, like rotten egg, but often not. A tell-tale sign of sewage pollution is any soapy, floral and fragrant smell from washing powder or detergent that’s made its way into our rivers from our homes.
  • Bubbles. Some foam forms naturally in rivers, particularly where a river is fast flowing. But if the foam is pure white with a fragrant smell, this is likely a sign of detergents from sewage pollution.
  • Orange colour. Mine water in a river can be quite distinctive and is often a vibrant orange colour. It can flow out of abandoned mines, bringing high levels of iron and other metals with it which can be damaging to river wildlife.
  • Oily, black or rainbow sheen. Road run off can look oily, blackish or have a rainbow sheen on the surface. Often this is washed off from roads and contains oil, brake and plastic tyre residues.

Plants and animals

  • Abundance of algae. It’s normal for there to be some algae in our rivers but too much is a sign of sewage or agricultural pollution, such as fertilisers and manure. Algal blooms or scums can make the water look bright green or blue-green (see image above), and sometimes the water surface appears dirty and crusty. Some algae can develop smells, described as spicy, fishy or grassy.
  • Sewage fungus. A gross-looking mass of slimy, bad-smelling, murky brown filamentous bacteria that thrive in nutrient-polluted water. If you see that coating the stones and in the water on the river, you can be pretty sure you’ve got water quality issues.
  • Dead animals, particularly fish. Often a tragic sign of a pollution event such as sewage discharges, oil or hazardous waste/chemical spills or agricultural runoff or pesticides.
  • Look for the bugs! Did you know that you can tell a river's health by the amount and diversity of invertebrates (animals without a backbone e.g. the bugs, flies, larvae, worms and snails) that live in it? River invertebrates are at the base of the food chain, food for fish and birds. A drop in their number has a knock-on effect on the entire ecosystem. Many are also sensitive to pollution, so they are used as "indicators" of water quality in rivers and lakes.
Bug samples in a big petri dish resting on grass
Bugs from a river in a petri dish
Credit: Sienna Somers

How to test water quality

Whether you’re a swimmer, a fisher, or someone who cares about the state of our rivers and the animals in it, there are ways you can check the health of your local patch.

Zoologist and campaigner Sienna Somers says: "With some basic equipment, such as wellies, a sturdy net, a tray and a good identification guide, anyone can start to build a picture of the health of their local river, lake or pond by searching for invertebrates.

"You can use a river invertebrate identification guide to help you identify which species you’ve found, or use a more in-depth guide like OPAL Water Survey to find invertebrates in your river or pond and learn how to use that data to work out your river’s health."

Alternatively, follow in the footsteps of Dr Geoff Sallis from Tewkesbury Friends of the Earth and start testing levels of nitrates and phosphates in the river (high levels indicate sewage pollution and/ or runoff from fertilisers).

Geoff's joined up with others along the Warwickshire Avon to regularly test the water quality in that stretch of the river and share their findings online.

"All people testing are volunteers and either members of environmental groups or individuals wanting to contribute. We use [the data] to raise awareness. We believe while national groups are maintaining awareness, it’s not convincing people locally, so we need to get people involved locally to put pressure on their MPs."

Geoff and his group use nitrate and phosphate testing kits from Hanna and Hach, and upload data to their website every couple of months. The objective? To hold water companies to account and campaign for our rivers to be better protected.

Right to a healthy environment

At the bare minimum, all water companies should be forced to share live data of sewage spills. It’s shocking that community groups are left to plug this gap in knowledge.

If the government enshrined our right to a healthy environment into law, everyone would have the right to access environmental data on their area (and make informed decisions about things like where to swim or fish). We’d also be better able to hold water companies to account for putting their profits over our health, our wildlife and our planet.

Show your support for a new Environmental Rights Act