Okay serious question, hear me out:
Why doesn't Russia have SSBNs in Lake Baikal?
Think about it. They'd be completely immune to American SSNs. Baikal, while not the ocean, is still massive, so there would still be considerable uncertainty about where exactly the submarines were. And even if the US did know, it's also an exceptionally deep lake, with an average depth lower than the max dive tolerance of Borei's, so they could just camp hundreds of meters underwater and be immune to any atmospheric detonations. Russia is very lucky to have something like this, China doesn't have any lakes anywhere near that size, and its biggest lake has an average depth of under 30 meters.
It's literally perfect. Totally survivable, totally flexible deterrent.
Why haven't they gotten on this?