Why this matters for the Dart: two very different dog products end up in the water, poo and pesticide, and both are within an owner's easy control.
The rules: bag it and bin it, everywhere, every time. And after a spot-on flea treatment, no swimming for at least four days.
Dogs love the Dart, and the Dart is mostly better for having them. The two problems are real but fixable.
Poo in the water
Dog faeces carry bacteria and parasites, and rain washes what is left on paths, fields and riverbanks into the water. UK dogs produce more than 880 tonnes of mess every day, on Keep Britain Tidy's estimate 62. The bacterial load is startling: Ireland's Environmental Protection Agency, whose catchment scientists have studied fouling around bathing waters, calculates that one dog poo contains enough E. coli to contaminate an Olympic-size swimming pool (around 3 million litres) to a level that would fail the Excellent bathing water standard, and that a single gram can contain up to 23 million faecal coliform bacteria 61. Those figures are Irish, but bacteria do not respect jurisdictions, and two Dart bathing waters are currently classified Poor precisely because of bacterial counts 4. Friends of the Dart's own testing measures E. coli across 31 sites 11; every uncollected poo near a watercourse is a small, avoidable contribution to the wrong side of that ledger.
Bag it and bin it, every time, everywhere. Any public litter bin will take a poo bag, and so will your bin at home. Do not leave bagged poo hanging on branches or beside paths; that is litter with a delayed fuse. In the South Hams, failing to clean up after your dog is an offence under the council's public spaces protection order, with a penalty of between £100 and £1,000; you can also be fined for not carrying the means to pick up 63. Why it helps the Dart: removed poo cannot wash into the river, and bathing water classifications are built from exactly the bacteria it contains. How hard: easy.
Carry spare bags, and consider the Green Dog Walkers pledge. Green Dog Walkers is a friendly, non-confrontational scheme run by dozens of councils: members wear a badge, always clean up, carry spare bags to share, and are courteous ambassadors rather than enforcers 60. Why it helps the Dart: gentle peer example changes more behaviour than signs do. How hard: easy.
Flea and tick treatments
This is the newer message, and it surprises most owners. Many routine flea and tick treatments, especially "spot-on" products, contain the insecticides fipronil and imidacloprid. They are excellent at killing fleas, and just as good at killing the freshwater insects that fish, birds and the whole river food web depend on. A 2021 study using Environment Agency monitoring data found fipronil in 98% of English river freshwater samples, and imidacloprid in 66%, with average fipronil concentrations exceeding chronic safety thresholds for aquatic life five-fold 56. The government's own monitoring confirms concentrations in surface waters that frequently exceed toxicity thresholds for aquatic insects, and in April 2026 it launched a call for evidence on tightening how these products are sold 57.
A treated dog sheds these chemicals for a long time. The Broads Authority notes that spot-on treatments can remain active for up to 90 days, and that the chemicals reach water not just when dogs swim, but when pets are washed, when their bedding goes in the laundry, and even when you wash your hands after stroking them 58.
Follow "Plan. Apply. Protect." This is the Veterinary Medicines Directorate's official advice for using flea and tick treatments while protecting waterways. The headline rule: do not let your pet swim in any water for at least four days after applying a spot-on treatment. Apply the product to the skin as directed, do not wash or let the animal swim immediately, and dispose of the pipette in the bin, not down the drain 55. Why it helps the Dart: the days straight after treatment are when the chemical load on the coat is highest. How hard: easy, it is a calendar note.
Ask your vet whether routine treatment is right for your dog. The British Veterinary Association advises that topical spot-on products should not be used on pets that are likely to swim or be bathed after treatment, and encourages vets to tailor flea treatment to each animal's actual risk rather than blanket year-round dosing 59. If your dog swims in the Dart weekly, say so at the consultation; tablets or a risk-based plan may suit better. Why it helps the Dart: a river full of swimming spaniels needs its owners and vets talking to each other. How hard: easy, one conversation.