Happens every summer, and this years no different, teacher drowned today whilst diving in a filled quarry. Happened very local to me maybe 3 years ago, 2 boys of around 18 that had been swimming in a reservoir all summer, one didn’t come back up, the other dived in to try and help, he didn’t either….

What causes this, I mind some theory of warm water being displaced and sort of flipped by cold water, pulling people under sort of like a current?.

Cold water shock.

http://completeguide.rnli.org/cold-water-shock.html

Cold water shock, snagging on debris, fatigue and steep sides, lots of things.

What he said + tangle hazards from scrap and vegetation.

I know that has its dangers, but those 2 had been swimming there all summer, and a body of water doesn’t change its temp very easily, over one day – they had been swimming there the day before.

Edit – aye, those factors too, what a horrible way to go….

Cold water shock.

Possible but doubtful if the person has become acclimatised to the ambient temp of the water.

Disused quarry. Tangled in bits of old machinery/wires/weeds?

It changes temp quite quickly compared to the sea, also you get some pretty extreme thermoclines

That one with the woman is only a couple of miles from me.
On the last day of high school my friends went for a swim in a small reservoir at the end of my road.
My best friend never came out 😥 .
He wasn’t the strongest of swimmers and became entangled in the weeds and couldn’t break free. Quite tragic.

They generally don’t have any shallow,so you are straight into deep water and as mentioned the thermocline can be significant, diving in can put you in very cold water

*goes away to Google thermocline*

My abiding memory of “puddle” sailing is how flipping cold they can be.

I don’t really understand the science but I recall being warned how long ponds took to warm up vs. the sea in the first half of the year.