Russia has dismantled a notorious facility dubbed the "whale jail" that kept dozens of the mammals in cramped conditions, causing an international outcry.

Almost 100 whales were kept in the secretive facility in Srednyaya Bay near the far eastern town of Nakhodka in 2018, before being released after an intense campaign by animal rights and environmentalist groups in 2019.

The animals were captured to perform in aquariums.

The environmental prosecutor's office of the Amur Basin – in the Russian Far East – said Thursday the jail had been completely dismantled.

"In order to prevent the illegal keeping of sea animals, the floating structures were dismantled," it said in a statement.

The structure of the jail had been moved to a shipyard "in a condition that excludes the possibility of their use for their intended purpose."

Environmental groups welcomed the move.

"It should have been done a long time ago," said Dmitry Lisitsyn, the head of the nongovernmental organization Sakhalin Watch that led the campaign against the jail.

"We put huge efforts into closing it and freeing the whales," he said.

All the whales kept in the jail, which included 77 belugas, are now in the wild.

Lisitsyn said the operation to free them was "very difficult" since most were babies that were not adapted to life in the wild.

They went through a rehabilitation program before being released into the Sea of Okhotsk separating Russia's far eastern peninsulas from Japan.

Lisitsyn said the jail was the only known such facility in Russia, but that the country has other places keeping large sea animals in "terrible" conditions for performances in aquariums.

Many of the whales held at the facility in Sredyaya Bay were to be sent to aquariums in China.