Well Olga, my maternal grandfather would swim at the beach in Aberdeen in January, but I think I am correct in saying that at that time of year the water was actually "warmer" than in May/June
If I am incorrect, no doubt somebody with greater knowledge than I will correct me
It reminds me of a story about a baby polar bear. He kept bugging his Mum asking her if he really was a baby polar bear, "not a black bear, a kodiak bear, a koala bear etc. She wouls reassure the little guy, but he persisted. So eventually she sent him to question his Dad. "Dad, am I really a baby polar bear, not a black bear ora kodiak bear etc." Response: "Now look here son, your Mum is a polar bear, I am a polar bear and you are a baby polar bear, so what is it that's bothering you?"
"Well Dad if I really am a baby polar bear, why is it that I am bloody freezing?"
In that respect, I am not the heroic grandson!