Seems the Russians take the exploration of Aquatica very seriously. Valdimir Putin himself has just gone down
"The dive is going perfectly, there is a perfect view with the lights," Mr Putin said from the depths of the lake on a crackling radio link-up during the dive.
However he expressed some surprise about how murky the water was in the lake, which contains around a fifth of the world's freshwater reserves.
"The water, of course, is clean from an ecological point of view but in fact it's a plankton soup, or so I called it," he said.
The Mir-1 is the same mini-submarine that in 2008 set a world record for the deepest dive in a lake by diving to 1680 metres (5512 feet).
Russian news agencies said Mr Putin had dived to a depth of around 1400 metres (4600 feet) - the deepest point in the lake's southern part - and safely returned to the surface after four hours underwater.