Almost 100 freshwater species not native to the UK have invaded the River Thames catchment making it one of the most highly invaded freshwater systems in the world, according to scientists at Queen Mary, University of London.

The research, published in the journal Biological Invasions at the weekend, suggests that legislation to prevent the introduction of non-native species across the UK has been unsuccessful. The cost to the British economy of invasive non-native species is Pounds 1.7bn every year (CABI report, 2010).

Lead author, Dr Michelle Jackson* who undertook the research as part of her PhD at Queen Mary, University of London, said: "We have identified 96 freshwater non-native species in the River Thames catchment and modern invasion rates (post 1961) reveal that one non-indigenous species is discovered every 50 weeks.

"Our research suggests that globalisation has facilitated species invasions because shipping activity and population size in the catchment had a positive correlation with the discovery of non-native species."

The River Thames is the second longest river in the UK, flowing through Oxford, Reading, Windsor and London before reaching the North Sea near Southend-on-Sea in Essex.

The researchers analysed pre-existing databases, field surveys, literature and atlases to establish a list of invasive species in the Thames.

"Invasive species are major drivers of biodiversity and ecosystem service loss, and multiple invaders have the potential to amplify one another's impact," Dr Jackson said.

"Our research highlights the need to establish how these multiple invaders interact."

The key legislation controlling the release (and escape) of non-native species in Britain is section 14 of the Wildlife and Countryside Act, 1981.