How did Gollum escape from Moria ?

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Originally Posted by Lastande Took

So Gollum climbed down the side of the chasm at the Bridge of Khazad-dum, swam across the water at the bottom, and climbed up the other side?

I would hope that that was not what was intended, as, even if possible, it would take Gollum time that he did not have. Better would have been to climb across the ceiling, if one contiguous pathway existed.