The ice bath and the compression from the water pressure cause constriction of blood vessels. This has been suggested as a mechanism that helps with the flushing of waste products, such as lactic acid, and reducing fluid accumulation from the affected tissue.
With the cold temperature, there’s a reduction of the metabolism and this can cause a slowing down of the physiological processes. The cold temperature will also reduce swelling and tissue breakdown. Ice water immersion is also said to be able to shift lactic acid.
Upon getting out of ice bath, the tissues and your body will begin to warm up, which causes an increase in circulation, which can assist in moving fluid and a relaxation of muscles in general.