Freshwater jellyfish discovered in the Moscow River have appeared there on account of the heat, a biology professor said on Wednesday.

Seven jellyfish belonging to the Craspedacusta species were netted in the Moscow River on Tuesday.

"This occurrence is absolutely normal... Their appearance is related to the increase in water temperatures," Nikolai Marfenin said.

Freshwater jellyfish sometimes appear in cooling pools at power stations because of the high water temperatures there, he explained.

Jellyfish have been netted in central Russia before. Last year, a resident of the Moscow region posted a video and photos of several jellyfish in his blog, saying that his daughter had caught them in a local pond.

Freshwater jellyfish are less than an inch in diameter and are not dangerous to humans.

A scorching heat wave has gripped much of European Russia since mid-June, sparking wildfires and causing the worst drought in decades.

MOSCOW, August 4 (RIA Novosti)