As signs of newly confident Russia, Russian scientists say they have broken the world record for the deepest dive in a body of fresh water, plumbing the depths of Lake Baikal in Siberia.
Russian news reports said two manned mini-submarines successfully plunged 1,680m (5,512ft) to the lake's bed.
The mission is part of a two-year plan aimed at conserving the ecosystem of Lake Baikal, which contains about one-fifth of the world's fresh water.
The area was declared a Unesco World Heritage site in 1996.
Russia's Interfax and Itar-Tass news agencies cited expedition organisers as saying that the Mir I and Mir II mini-submarines had touched the bottom of the lake.
"This is a world record for a submarine diving in fresh water," Interfax quoted an organiser as saying. However, the Russian team say they are still awaiting official confirmation of the depth of the dive.
The Mir capsules are already in the record books for their undersea expeditions - descending to depths greater than 4,000m.
Before the expedition set off, leader Artur Chilingarov described it as a complex one. "There are technological problems, fickle weather conditions. Fresh water dictates its own special conditions," he said.
The two 18-tonne mini-submarines were designed to operate in seawater - but have shed hundreds of kilos to make them buoyant enough in less dense fresh water.
Mr Chilingarov also led a team of scientists to the North Pole in August last year - where they controversially staked Russia's claim by planting a flag on the seabed.
Environmentalists had expressed concern that Russia intended to exploit the lake's mineral wealth, but expedition leaders insisted the mission was for research and conservation purposes only.
Mr Chilingarov said his team would put together "a package of practical measures and recommendations" to promote conservation of the lake.
Lake Baikal, formed 25 million years ago, is home to hundreds of species of flora and fauna. One of the most unusual animals unique to the lake is the Baikal seal - one of the few seals to spend its life in fresh water.
