Quagga mussels are considered one of the UK's most problematic invasive species
London's water pipes have got clogged up by the equivalent of more than four Olympic-sized swimming pools of invasive mussels.
Thames Water says it spends more than £6million each year clearing freshwater Quagga mussels from pipes, with engineers often uncovering hundreds of thousands of shellfish during a single maintenance operation.
Quagga mussels, native to the Dnieper River basin in Eastern Europe, are considered one of the UK's most problematic invasive species.
Their rapid rate of reproduction makes them incredibly difficult to manage, with a single mature mussel capable of producing up to one million eggs during a breeding season.
Once established, the mussels attach themselves to hard surfaces in dense colonies, coating the inside of water pipes, pumps and other infrastructure.
As the colonies grow, they restrict water flow, reduce operational efficiency and increase the risk of service disruptions across the network.
Thames Water said the scale of the problem has intensified in recent years, forcing engineers to implement specialist methods to remove the shellfish.
Maintenance teams now routinely use high-powered hydro-blasting equipment to clear heavily infested pipes, while divers are sometimes deployed to tackle severe blockages.
The company warned that Quagga mussels are only one of several species threatening its assets, with signal crayfish and Chinese mitten crabs also creating challenges.
Both species are prolific burrowers, tunnelling into riverbanks and around water infrastructure.
Their activity can accelerate corrosion, increase the build-up of silt inside pipes and channels, and raise the risk of flooding by reducing the capacity of drainage systems.
Beyond the impact on infrastructure, the species also pose a wider environmental threat.
Invasive non-native animals can outcompete native wildlife for food and habitat, disrupting ecosystems and reducing biodiversity in rivers and waterways.
Alexandra Collington, Thames Water's biosecurity and invasive non-native species officer, said the company was facing an escalating challenge.
"Quagga mussels may be small, but the impact they have on our network is anything but," she said.
"Whether crabs or crayfish, we see non-native invasive species damaging our infrastructure and causing disruption.
"They pose a significant threat to native wildlife and biodiversity, affecting the health and balance of our ecosystems.
"We've committed over the next few years to increase our work tackling the impact invasive species have on our infrastructure, so that our network remains safe and we can protect our waterways and wildlife."
The company said managing invasive species is becoming an increasingly important part of maintaining reliable services, with climate change and warmer water temperatures also contributing to the growing challenge.
As infestations become more widespread, Thames Water expects investment in biosecurity measures and specialist maintenance to remain a key priority in protecting essential water supplies, and reducing the risk of disruption for customers.
