The Rivers Trust logo
A blue tit looks at a bundle of animal hair it has collected

From our rivers to birds’ nests: how pet flea treatments are impacting the environment

What’s the link between our waterways, our dogs, and the decline of our songbirds? Learn about pet paraciticides and chemical pollution with this guest blog by Emma Phipps from SongBird Survival 

Explore
The Rivers Trust

21/07/26

With the warmer months in full swing, many pet owners are thinking about protecting their animals from fleas and ticks. For many years treating monthly has been seen as a routine part of responsible pet care – but in protecting our pets, are we are also inadvertently damaging the wider environment. 

A hidden source of pollution 

For years, scientists have documented how a cocktail of chemicals is polluting UK rivers, many of them toxic to aquatic life. While pesticides are often associated with farming or gardening, there’s another, less obvious source: the treatments we apply directly to our pets. 

Many common spot-on flea and tick treatments contain the pesticides fipronil and imidacloprid - fipronil is classed as a persistent “forever chemical,” while imidacloprid is so toxic that just one teaspoon could kill 1.25 billion honeybees. Although both pesticides have been banned for agricultural use in the EU, they are still widely used in pet treatments and are increasingly detected in the natural environment – including in water samples taken from rivers. 

Recent research from the University of Sussex, commissioned by SongBird Survival, examined blue tit and great tit nests and found that every single one contained insecticides. Fipronil was detected in all nests studied, and imidacloprid in over 80%. In total, between two and eleven different chemicals were detected per nest. 

So how do pesticides get into birds’ nests? Well, many birds use animal fur to line their nests.  and the study found that pesticides can transfer from nesting material into eggs and chicks, with higher concentrations linked to increased mortality rates. 

baby blue tits are in a nest lined with fluff and fur
Blue tits, along with other birds, have been known to use pet hair which is contaminated with flea treatment pesticides to line nests Credit: Dr. Cannelle Tassin de Montaigu

Impacts on ecosystems 

The problem doesn’t stop there. These chemicals are also entering rivers, especially in urban areas, where in-water concentrations often exceed safe limits. This is having a knock-on effect on aquatic insects, with studies showing declines of up to 90% in species like mayflies and caddisflies as imidacloprid levels rise.  

These insects play a vital role in supporting biodiversity, so their loss can trigger cascading effects through the ecosystem. Songbirds such as dippers and grey wagtails, for example, often seen hopping along riverbanks and wading in shallow streams, rely on these insects for food. Combined with other threats, as their main food source dwindles these birds are finding it harder to breed successfully. Both species are now struggling, with population declines of 52% and 11% respectively from 1995-2024. 

A small brown bird with a white throat stands on a rock in a flowing river
Dippers eat insects that live in our rivers, numbers of which are impacted by chemical (including pet pesticide) pollution in the water

How can we make change happen? 

SongBird Survival recently partnered with charities Buglife and WildFish to write to Defra regarding this issue. The letter signed by The Rivers Trust, along with over 30 other conservation organisations and academics, called for a number of changes around how these pesticides are regulated. The full letter, featured in an article by The Guardian, is available to read here. 

Encouragingly, the Veterinary Medicines Directorate is looking into the potential of restricting how pet products containing fipronil and imidacloprid are sold, while the House of Lords is gathering evidence on how veterinary parasiticides are affecting the environment. Outcomes expected later this year could influence how these treatments are used and regulated in future. 

A black dog stands in a shallow river
Keeping treated dogs from swimming in rivers can prevent pet pesticides from damaging the freshwater environment

Simple steps that can make a difference  

So, what can pet owners do now? Small changes can make a real difference. 

  • Avoid swimming: if you use a spot-on treatment for your dog, don’t let it swim in rivers or other water sources. Studies have found that fipronil and imidacloprid can remain on fur for up to 28 days. 
  • Dispose of pet fur carefully: if you treat your pets, avoid leaving their fur outside where birds may collect it for their nests. 
  • Always pick up dog waste: remember to pick up, bag and bin your dog’s poo, both on walks and in your garden. Even tablet-based flea treatments can enter the environment through animal waste. 
  • Speak to your vet: ask about the most appropriate approach to flea and tick treatment. If your pet is at low risk, treatment may not always be necessary or could be limited to certain times of year. 

Looking after our pets is essential, but so is protecting the wildlife and freshwater environment around us. By being more aware of the wider impact of flea and tick treatments, we can take simple steps that help safeguard both.  

 

Blog author Emma Phipps is the Scientific Research and Impact Manager at SongBird Survival, which is the only charity dedicated solely to reversing the decline of the UK’s songbirds. The charity works to change the future of songbirds by funding research into the causes of the decline and creating solutions. 

 

References  

Hadley, M. et al., (2026) Occurrence, patterns and previously overlooked sources of three veterinary ectoparasiticides in rural and urban Welsh rivers. Environmental Pollution, 394 

Miller, J. et al., (2020) Common insecticide disrupts aquatic communities: A mesocosm-to-field ecological risk assessment of fipronil and its degradates in U.S. streams. Science Advances, 6(43) 

Tank, P. et al., (2026) Ubiquitous presence of pesticides in feathers of common UK birds. Environmental Science and Pollution Research, 33, pp. 7059-7069 

Tassin de Montaigu, C. et al., (2025) High prevalence of veterinary drugs in bird's nests. Science of The Total Environment, 964 

Tassin de Montaigu, C. et al., (2026) Transfer of veterinary parasiticides from the fur lining bird’s nest to eggs and chicks. Environmental Science and Pollution Research, 33, pp. 7070-7081 

Wildlife and Countryside Link (2023) Toxic chemical cocktails found at over 1,600 river and groundwater sites across England. Available here: https://www.wcl.org.uk/toxic-chemical-cocktails-in-rivers-across-england.asp 

Dog flea treatment

Flea-mergency: Pet treatments taking a bite out of the health of England’s rivers

  • Water Quality

The delicate balance of life in our rivers is under threat, and it’s not just due to pollution from factories, sewage or agriculture. Surprisingly, one of the culprits is our beloved pets.

Learn more

Join our newsletter

Sign up to receive our supporter newsletter and get monthly updates on our work, campaigns, news (and future competitions!) directly to your inbox.

Sign up to our newsletter
Back to top
Help us improve