Before the cold, the breath is the only variable you fully control. Set it deliberately.
Four counts in through the nose. Six counts out through the nose. The longer exhale is the point — it settles the system that the cold is about to startle. Do this for a minute before you enter and the plunge meets a body already at its floor, not one bracing at the edge.
In the water, keep the exhale long and the count slow. The urge is to gasp and grip. The practice is to breathe out, and out, and out.
The cold does not get warmer. But the breath decides whether you are in it or fighting it.
A reading from Meridian.