Blue Lake is one of the deepest lakes in Russia, if not the world. It’s what’s called a Karst Lake – a lake with no visible stream running to or away from it. It’s instead fed and drained by a series of underwater caverns and passages. This also gives the impression hat the lake is bottomless, as they’ve yet to find the underwater streams hat feeds the lake, nor the true bottom. In fact, what they think ‘might’ be the bottom, may just be a shelf over a larger cavern beneath the “floor” of the lake.