Toxic Mudflows Threaten the World's Deepest Lake Which Contains 20 Percent of the Planet's Unfrozen Freshwater

The oldest and deepest lake in the world is under threat from toxic mudflows after severe flooding in the Russian region of Siberia, environmental campaigners have warned.

Lake Baikal—located in a mountainous region of southern Siberia north of the Mongolian border—was formed between 30 and 25 million years ago and has a maximum depth of 5,387 feet.

It is the seventh largest lake in the world by surface area and largest freshwater lake by volume. In fact, Baikal contains more than 20 percent of the planet's fresh unfrozen surface water.

But flooding in the Siberian town of Baikalsk—which lies on Baikal's banks—has affected a former Soviet pulp and paper mill, which could lead to the washing of toxic chemicals into the lake's pristine waters, considered among the world's clearest.

Campaigners say this would lead to an ecological catastrophe, posing a huge threat to the unique animal life in the lake, The Siberian Times reported. It is home to nearly 2,000 endemic species, those that are found nowhere else in the world.

While the mill was shut down in 2013, there are still 13 storage ponds which contain untreated waste from the production process. Three of these lie right on the banks of the lake, three others are located to the east, while the remainder lie slightly uphill on higher ground, according to Dave Petley from the University of Sheffield in the U.K.

Experts say there is a risk that the waste stored in these ponds could be washed into the lake by floodwaters.

"The potential threat here lies in the setting of the waste ponds," Petley wrote in a blog post for the American Geophysical Union. "The whole site is located on an active fan fed by the channel that emerges from the mountains. It is entirely reasonable, based upon the morphology, to assume that this channel is subject to flash floods and debris flows. In these systems, one would expect that high volume flows will overflow the channel and migrate across the fan. If so, the first waste pond in the staircase would be at high risk of being inundated."

"The potential consequences of such an event entering the highest waste storage pond should be clear—the likelihood of a very large debris flow breaching the first waste pond looks to be very high indeed," he wrote. "This pond would probably fail, inundating the next one downslope, and so on. Thus, it is entirely feasible that seven or more storage facilities could fail, releasing the waste into the lake. Of course, the three ponds to the east are also vulnerable."

In total, the ponds contain about 6.2 million tons of waste, with Petley describing the risks at the storage site as "unacceptably high."

"The consequences of a major failure into Lake Baikal at Baikalsk would be truly catastrophic. And it is worth noting that these are not the only waste storage ponds in this area," he wrote.

The last disastrous mudflow into Baikal took place in July 1971, which washed more than 12 miles of the Trans-Siberian railway into the lake.

Baikalsk paper mill
Baikalsk Paper Mill on Lake Baikal, August 11, 1991. David Turnley/Corbis/VCG via Getty Images