Thames River Invasive Species: Freshwater Species of the Week

The Thames River is among the most invaded by invasive species. Photo: Cnbrb/Wikimedia Commons


It seems that London was host to more than Olympic athletes, as a recent study suggests the Thames River is among the world’s most invaded freshwater systems.

Research published in the delightfully named journal Biological Invasions found nearly 100 invasive species living in the Thames. The researchers at Queen Mary, University of London concluded that recent legislation to stem the tide of invaders isn’t doing enough.

The researchers estimated the impact of invasive species in the Thames at $2.7 billion a year (£1.7 billion).

Researcher Michelle Jackson pointed out that the team identified 96 freshwater invaders. She added that, since 1961, one new invasive species was found every 50 weeks, on average.freshwater species of the week

The high rate of invasives perhaps isn’t too surprising, since London has long been one of the world’s major shipping centers, and sees heavy traffic from across the globe. Invasive species are frequently transported by international shipping, especially when they are taken in, or released, in ballast water.

High historic levels of pollution and heavy use of the Thames’ resources have also put untold stresses on native populations, making it easier for invasives to gain a foothold. In turn, many invasive species make it harder for natives to return, since they can outcompete them or prey on them.

Every November, the Zoological Society of London and partners do a survey of invasive species in the Thames, after part of the river is allowed to drain naturally.

Some of the species ZSL has catalogued include the Chinese mitten crab, zebra mussels, and the Asiatic clam. Other species are plants and other invertebrates.

According to the ZSL, defense methods include “exchanging ballast water in the open ocean, chemical treatment using biocides, heating ballast water, filtration and using UV light. Unfortunately none of these methods are 100% effective and can be very expensive. Certain methods, such of the use of biocides can also have harmful effects on the external environment.”


Brian Clark Howard covers the environment for National Geographic. He previously served as an editor for and E/The Environmental Magazine, and has written for Popular Science,,,, Yahoo!, MSN, and elsewhere. He is the co-author of six books, including Geothermal HVACGreen LightingBuild Your Own Small Wind Power System, and Rock Your Ugly Christmas Sweater.