Obviously the water was too cold!
I remember when when my son brought his bride here for Thanksgiving when they'd just been married about 6 months. I was still cleaning up dishes when I heard a commotion in the driveway and noticed my 2 sons and husband out in the snow. I went to check and was ushered insside without figuring out what was happening.
About 20 minutes later, they came inside and my son whispered that they were shooting hoops and his wedding ring flew oww and landed in a snow bank. They found it and I was sworn to secrecy so that his new bride wouldn't find out.
Shrinkage!
I’m sure sifting through the sandy bottom looking for good flat rocks to skip was the main problem.