The Ukrainian Greek Catholics in Knoxville do this too, or something like it. The priest throws the crucifix in the Holston River, (or rather, it's a branch of the Holston) and the teen boys all jump in and try to find it, which means of course they have to go feel around with their feet--- or if it's more than head-deep, go to the bottom! The young fellow who finds it is the hero of the day, of course: much laughinbg and back-slapping, and everybody chanting and doing metanias.
Of course the Holston is nowhere near as cold as the Neva. Usually no ice, even.
One thing in this great video surprised me: the girls!! I never thought girls would have been allowed to do this, especially in Russia.
Well, times change...
Throwing in a gold cross and then having the local boys retrieve it is a Greek tradition. Of course in Greece it is generally warmer than just about anywhere in Russia. As K likes to say, “the Greeks are the fun part of the Church.”