Project status
Marine and Freshwater
UK and Europe
Contact details

At ZSL we work tirelessly with partners and volunteers in the Thames estuary and the wider river catchment to protect and better understand the species that are found here, including invasive non-native species (INNS). 

A close up of a mitten crab

Why are there invasive species in the Thames?

The River Thames is particularly vulnerable to introductions of invasive non-native species (INNS) due to the dense human population and high level of marine traffic, and is now one of the most heavily invaded river systems in the world. Invasive species arrive in British waters via several means:

  1. Ballast water. Ships takes up ballast water in order to increase stability when crossing the open seas. This water can contain the larvae of local plant and animal species. When the ship reaches its destination in a foreign country, these plant and animal larvae are expelled from the ships’ tanks along with the ballast water.
  2. Biofouling: Adult species attach onto the hulls of ships in a process known as ‘biofouling’.
  3. Trade in the aquaculture industry has also resulted in the importation of foreign species.

With suitable environmental conditions these species can colonise new waters. In the absence of predators, parasites or competition, populations of invasive species can rapidly multiply, exhausting resources used by native species or severely degrading their habitats.

How is ZSL monitoring invasive species in the Thames? 

Since 2006, ZSL has been monitoring invasive species in the Thames as part of a long-term collaborative project. We want to know if any new species arrive in the river and how these new arrivals interact with the native species.

Richmond river bed survey

Every year in November, the weir at Richmond Lock is lifted to allow a portion of the river to drain naturally at low tide. We use this opportunity to scout the river bed for any species that are not native to this country's waterways. During the 2014 survey, the invasive quagga mussel (Dreissena rostiformis bugensis) was identified for the first time. This part of the river is home to populations of rare freshwater mussel, so it’s especially concerning that the quagga’s arrival will add to the pressures that threaten their future.  

A quagga mussel


People and partners 

ZSL's Anna Cucknell, Joe Pecorelli and Thea Cox work on Thames projects in partnership with the Thames Landscape Strategy

Key species

  • Chinese mitten crab (Eriocheir sinensis)
  • Asian clam (Corbicula fluminea)
  • Zebra mussel (Dreissena polymorpha)
  • Quagga mussel (Dreissena rostiformis bugensis)
Thames conservation

Our Thames invasive species project is just one of the ways we’re working to conserve wildlife in the UK. 

Aquatic invasive non-native species

  • Aquatic invasive non-native species (INNS) are considered by the IUCN to be the second biggest threat to biodiversity. 

  • Since 2006, ZSL has been monitoring invasive species in the Thames as part of a long-term collaborative project. 

  • A group of citizen scientist volunteers in a river
    Support our Thames conservation work

    Thames Conservation

    The river Thames is not only a busy urban waterway but is also home to a fascinating and often unexpected array of wildlife.

  • Four ZSL conservationists study fish and record results on the Putney foreshore
    Thames conservation

    Fish conservation in the tidal Thames

    We've conducted the most comprehensive studies of juvenile fish in any estuary in the UK, and tagged the first fish to swim through central London.

  • Spurdog shark in the Thames
    Did you know there are sharks in the Thames?

    The Greater Thames Shark Project

    Working together with anglers to better understand the importance of the Thames estuary to these animals and to ensure their long-term survival in the wild.  

  • conservationists_wading_through_river
    A vital habitat for wildlife

    London’s Rivers

    Please help us health-check and survey our rivers as part of our ongoing programme of Citizen Science projects.

  • Support ZSL with a donation today