When I was a teen we used to swim in what were called locally “blue holes”, essentially abandoned rock quarries that had filled with water. We would jump off ledges 20-30 feet high, some where you had to run off to clear other rocks below. There would be the occasional drownings when someone got trapped below under a ledge (none when I was ever around). We were always warned against going there but we were teens.
Thermalclines are a danger in Rock Quarries also. Rapid drop in Temps at certain levels can cause muscle cramping.
We did the same thing here in NH. There are many abandoned granite quarries around here. Some of them have over 100’ of water in them. One has train cars at the bottom.
There are a pair that are separated by a wall of rock about 10’ thick. There is a hole/cave that connects them about 20’ under the water line. The big thing to do was dive down and swim from one into the other.
We also had cliff/walls to jump off. I jumped off the 30’ a couple times. There was also a 60’. I never stepped off of that one.
There was another quarry that had a gravel road right up to the edge. If a car got stolen, many times it would go right off that edge. It was 60’ straight down from there I was told. I remember going back there one time and seeing tire tracks going right up to the edge and then....
This was back in the 1980’s or before. Most of them now have been fenced off. The twin quarries have houses built right around them now. One house was built so their deck with diving board and slide extend over the water. Pretty cool, but I bet their homeowners insurance most be high.