April 7, 2008—There's something fishy in London, and it's not the city's trademark fish and chips.

Short-snouted seahorses have set up residence in the recovering River Thames, conservationists announced today.

The fish—pictured above in the London Zoo aquarium—were found in recent surveys that assessed the health of the once heavily polluted river.

The discovery of the animal in brackish tidal waters as far upriver as London was kept under wraps by the Zoological Society of London (ZSL) until the species had been granted protected status. Little data are known about the seahorses' populations.

Conservationists had feared that the bizarrely shaped fish might attract unwanted attention, such as from aquarium-trade collectors, said the ZSL's Alison Shaw.

An increase in plankton due to Climate change and warmer sea temperatures may help explain the seahorses' appearance in the river, according to Shaw.

The government declared the Thames biologically dead in the 1950s, and various groups have worked to rehabilitate it for the past two decades.

These efforts have led to "a vast improvement" in the Thames' water quality, Shaw said.

"This latest discovery demonstrates the importance of the Thames estuary as a wildlife habitat."

Seals, dolphins, salmon, and sea lampreys have also been seen swimming in the healthier river.

—James Owen