Thames Invasive Species

INNS Survey

Aquatic invasive non-native species (INNS) are a serious problem across the globe and are considered by the IUCN to be the second biggest threat to biodiversity. The River Thames is particularly vulnerable to introductions of 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.

Since 2006, ZSL has been monitoring the 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. Find out more about the discovery of quagga mussels in the Thames.

Environmental DNA research

In partnership with Kingston University, ZSL is developing new methods to identify invasive non-native species by taken water samples and identifying environmental DNA (urine, scales, other biological material). This method will be a cost-effective way to monitor invasive species. 



Quagga Mussel
The invasive quagga mussel was found in the Thames for the first time in 2014

Project information

Key species

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


PDF icon Invasive Species Report 2017 (1.05 MB)

People involved

Joe Pecorelli works on the Thames Invasive Species project. 

Partners and sponsors

  • Marine Conservation Society
  • Thames Landscape Strategy