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Pollution of our waterways is a hot topic, and one that rightly sits at the forefront of public concern. Across Dorset, our rivers are in a worrying state, with only 15% in good ecological health and none in good overall health. A combination of agricultural practices, water treatment processes, industrial discharges and even our everyday activities has left our waterways in decline.

Pollution affecting rivers can broadly be divided into two main categories: point source pollution and diffuse pollution.

Point source pollution comes from a single, easily identifiable origin that discharges directly into a river or stream. This includes treated and untreated sewage released through storm overflows, animal waste from intensive livestock farming, and chemical or heavy metal discharges from industrial facilities.

Diffuse (or non-point source) pollution, on the other hand, doesn’t come from one place. Instead, it builds up gradually across the landscape as rainwater and surface runoff carry pollutants into rivers, streams and lakes. Although more difficult to trace, diffuse pollution can be equally — and often more — damaging to the health of our waterways.

Agricultural runoff is one of the most common forms of diffuse pollution. Fertilisers, pesticides and herbicides applied to farmland are washed into rivers during rainfall or irrigation. These substances add excess nutrients to the water, causing eutrophication — a process where oxygen levels drop and algal blooms thrive, suffocating fish, invertebrates and other aquatic wildlife. Harmful chemicals within these products can also directly impact the delicate balance of freshwater ecosystems.

Urban runoff, sometimes referred to as ‘people pollution’, is another major contributor — particularly in built-up areas. When it rains heavily, stormwater from streets, car parks, construction sites and gardens collects grease, oil, heavy metals and chemicals before entering drains that flow straight into rivers. Everyday household activities, like washing cars with detergents or applying garden chemicals, may seem harmless, but all contribute to the slow accumulation of pollutants entering groundwater and waterways.

A less visible but equally serious threat comes from pharmaceuticals and pet treatments. Hormones and chemicals from human medicines make their way into rivers through wastewater systems, while insecticides used to treat pets for fleas, ticks and worms have been detected in concentrations exceeding safe limits for wildlife. Many pet owners are unaware that allowing treated animals to swim or drink from rivers can release these toxic substances directly into the water.

Because diffuse pollution builds gradually and originates from numerous small sources, it is significantly harder to identify and control than point source pollution. The absence of a clear single origin makes it challenging to monitor and address, but awareness and community involvement can make a huge difference.

Despite the challenges, there is hope. Across Dorset, individuals and communities are stepping up to help safeguard our waterways. At Dorset Wildlife Trust, we’re working to monitor river health and reduce the impact of pollution through a growing network of citizen scientists.

We currently coordinate two volunteer-led initiatives, Water Guardians and Riverfly Monitors, both designed to monitor the condition of Dorset’s rivers and detect pollution as early as possible. These projects also play a crucial role in raising awareness about the pressures facing our freshwater habitats.

The Water Guardians project, run in partnership with Wessex Water, trains volunteers to recognise visible signs of pollution and report them promptly to the relevant authorities such as the Environment Agency, local councils, and water companies. Each volunteer is assigned a stretch of river to monitor regularly. During their monthly walks, they look for signs such as oily residues, sewage discharges, soapy foam, waste, or broken infrastructure. Many also pick up litter, report fly-tipping, and record the presence of invasive non-native species like Himalayan balsam, along with any wildlife they encounter.

By acting as the “eyes and ears” of Dorset’s rivers, Water Guardians ensure that pollution incidents are identified quickly and that action can be taken before serious harm occurs. Their local knowledge and consistent presence make them an invaluable part of Dorset’s pollution response network.

Our second group, the Riverfly Monitors, take a more hands-on approach to measuring river health. These volunteers are trained to sample and identify a range of aquatic invertebrates, species that serve as natural indicators of water quality. Using a method known as ‘kick sampling’, volunteers wade into rivers and gently disturb the riverbed, catching invertebrates such as stoneflies, mayflies and caddisflies in a net for counting and identification.

These species are extremely sensitive to pollution, so changes in their abundance or diversity can reveal issues long before they become visible. Each monitoring site has a designated ‘trigger level’ — if a survey finds numbers lower than expected, the Environment Agency is notified to investigate potential pollution sources.

This long-term data collection helps build a clear picture of the health of Dorset’s rivers, providing early warnings of pollution and helping track improvements over time. It also fosters a strong connection between local people and their natural environment, empowering communities to take an active role in protecting their waterways.

Together, Water Guardians and Riverfly Monitors are making a real difference. Their combined efforts enable faster responses to pollution incidents, protect rivers from prolonged damage, and contribute to the wider recovery of Dorset’s freshwater ecosystems.

Pollution may still pose a serious challenge, but through citizen science, partnership, and community action, Dorset Wildlife Trust is helping turn the tide. With continued awareness, monitoring and collective effort, we can restore our rivers to good health — for wildlife, for people, and for future generations.