Cold water temperature varies hugely, and while this isn't scientific, anecdotally, open water swimmers experience it in these bands.
Open-water swimming: a beginner's guide
9 great cold water swimming tips – Vivida Lifestyle
Can you tell how cold you are? – Outdoor Swimming Society Outdoor Swimming Society
THE THRILL OF THE CHILL
Yoga for winter swimming – Outdoor Swimming Society Outdoor Swimming Society
Should you stay in cold water for one minute per degree of water temperature? - Outdoor Swimmer Magazine
How Cold Is Too Cold When It Comes To Swimming?
A Brief Guide to Bay Area Open Water Swimming — Odyssey Open Water
9 great cold water swimming tips – Vivida Lifestyle
It's time to start preparing for winter swimming - Outdoor Swimmer Magazine
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What to wear cold water swimming - Travel with Kat