Local vet warns that dogs swimming in rivers can cause danger to both dogs and the river

A vet based in Molesey says treatments used to treat worms and fleas can wash off in the river causing water pollution

Author: Will HarrisPublished 15th Aug 2026

A local vet has been telling us the dangers that can come from dogs swimming in rivers, for both the dog and the river

Vanessa Waite is Head Vet at the Vet Station in Molesey, she says she's seen a considerable increase in cases resulting in dogs swimming in water

"You can get ingestion of dirty waters in some place, which could generally lead to vomiting, diarrhea, bugs. So we do see an increase of that in summertime, unfortunately.

Particularly around the vet station, the River Mole, we get a lot of pad injuries, so they sometimes cut their paws in the river. If a dog has a wound, they can get infections."

However Vanessa also told us about the damage dogs could be doing to the river itself

"In March 2023, the Grantham Institute published something regarding the fact that flea and worm treatments and tick treatments in dogs primarily were getting washed off into the waterways and these substances that are banned in agriculture because they are toxic to, for example, bees.

What they found is that levels as low as 0.013 microgram per litre can be damaging for aquatic communities and ecosystems. And the samples that they took had actually got levels of 1 microgram per litre, so significantly higher than what's toxic"

Vanessa offers advice for anyone with pets with flea or worm issues that love to swim

"If your pet has had a spot on treatment to prevent fleas, worms and ticks, to not allow them into waterways.

If you have a dog that swims a lot, maybe switch to an oral treatment instead. Clean up urine and faeces as much as you can because it can be excreted in those places. And again, we don't want those entering our waterways."

However Vanessa says in order for things to actual change and for the waterways to be protected over the long term, we need to change how people get hold of these treatments

"The British Veterinary Association, advised that we should be more careful with the prescriptions of flea and worm and tick treatment, and that we should take them off the shelves, because these can actually be bought over the counter, not just on prescription from vets.

Vets should do risk analysis before they sell these products, so historically, we've all been treating a sort of like a blanket treatment, use this preventatively, apply this once a month.

But these studies are now showing that this is damaging our aquatic systems, our rivers, our waterways, and it's damaging to the ecosystems there."

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