As Water Temperatures Rise, Freshwater Jellyfish Found in British Canal

A freshwater jellyfish (Craspedacusta sowerbii).

A freshwater jellyfish (Craspedacusta sowerbii). JT/Wikimedia

Following weeks of scorching heat in the United Kingdom, a small transparent freshwater jellyfish that thrives in warm waters has been found in a British canal. Harmless to humans, the jellyfish, Craspedacusta sowerbii, is native to the Yangtze basin in China, but has spread to waterways worldwide over the last century. 

In recent decades, the species has become an increasingly common sight as global temperatures rise, particularly in late summer when waters exceed 20 degrees Celsius (68 Fahrrenheit.)

The recent jellyfish bloom in England is in the Middlewich branch of the Shropshire Union Canal.

“It’s thought that the hot and sunny weather could have encouraged the jellyfish to these parts and created perfect conditions for them,” Sara Hill, an ecologist at the Canal & River Trust, told the Guardian. “But we don’t know whether they will make their permanent home here so we’re finding out as much as we can.”

Freshwater jellyfish first arrived in Britain in the 19th century when explorers brought back plants and animals from their travels. Summer sightings have increased in England since the 1980s in canals, shallow freshwater lakes, and flooded quarries as high water temperatures have become more common. In previous years, the species’ main “blooms” appear in August and September, and disappear by October.

Blooms of these freshwater jellyfish have also been increasingly observed across Canada and the United States, particularly in the Great Lakes region; several parts of Europe, including Ireland, Sweden and Lithuania; in southeast Asia; and even as far as Patagonia in Chile and Argentina.

—Christian Detisch