Novosibirsk cavers had their expedition in Altay mountains between 2010.3.13-20. The main event was cave diving at the bottom of Altayskaya cave (-240m depth ,4175m length). Unfortunately the siphon quickly became impassable at -2m. Many other exploration activites were carried out like climbing and digging. original info here
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Strictly speaking the siphon being explored was not at the bottom, but in the end of accending side branch of the cave (Veselukha system).