Two Russian environmental groups have closed, activists said Friday, blaming a 2012 law requiring them to register as "foreign agents" for making it impossible to operate.

"It's impossible to work, it's simpler to just close the organisation," said Maksim Vorontsov, a former co-chairman of Baikal Wave, an organisation created in 1990 to protect Siberia's Lake Baikal, the world's oldest and deepest lake which is home to unique wildlife.

"Let it remain in people's memories, it was a 25-year run that people can remember fondly," he told AFP, adding that the paperwork to dissolve the organisation -- one of the first environmental groups in the post-Soviet era -- was sent to the justice ministry on Friday.

Dront, another decades-old environmental organisation based on the Volga river in Nizhny Novgorod, said Friday it was "stopping its activities indefinitely, until the stigma of 'foreign agent' is removed."

They were the latest groups to close after Russia's parliament passed law in 2012 that required all non-governmental organisations (NGOs) that receive foreign funding and engage in "political activities" to register as a "foreign agent" or face massive fines.

The 2012 measure, which was denounced by international rights groups, has been gradually rolled out and most environmental groups were not targeted until last year.

Both environmental groups also have to pay a fine of 300,000 rubles each (about 3,500 euros/$3,900) for not declaring themselves "foreign agents".

Although Baikal Wave received small grants from foreign foundations in the past, its finances have always been transparent and the money was not used to advance any political agenda, he said.

He said among the projects singled out by the ministry as evidence of their guilt was a foreign grant they used to build bio-toilets on the shore of Baikal, which has few facilities and annually gets overrun by campers.

The ministry also referred to online posts and remarks made privately to prove the organisation was "political," he said.

"If I build toilets in 2012 and then go to a hearing on a landfill project in 2015... a normal person would not see a link there, that I used money for toilets to influence public opinion," he said.

"But the ministry sees this link."

In January, a state-appointed rights ombudsman in the region, Valery Lukin, wrote an appeal saying Baikal Wave should not be in the register and that the group's work has been "only positive".

Since November, Baikal Wave has tried to fight the justice ministry's decision to add them to the register of "foreign agents" because the tag would harm the group's reputation and make it impossible to work with state institutions, Vorontsov said.

"Since November, we have been running around courtrooms and justice ministry offices, filling out papers" instead of hosting workshops, giving lectures and engaging in environmental cleanups, he said.

"We spend time, energy and money on this... all we do is paper pushing" often just to have documents sent back due to a "checkmark in the wrong box," he said.

More than 115 NGOs currently feature on the justice ministry's list of "foreign agents."