It's an effect that's been widely described and studied.
A meta-study says:
Prolonged survival under water
Generally, drowning results in cardiopulmonary arrest within 2 min (Fainer et al. 1951). Quan et al. (2014) reported on the outcome of 1094 open water drownings; most (78%) had bad outcomes (74% death, 4% severe neurological sequelae), and of ...