No swimming?

On our way to hike in Jogyesan Provincial Park yesterday, we passed a dam and a huge dammed lake. It was breathtakingly beautiful (I realized later that I probably found it especially serene due to the lack of clear cuts on the surrounding mountains). As we were driving by, I tried to ask about going swimming in the lake. ChiHo was having trouble understanding what I was getting at; both he and EunJu couldn't understand why I would possibly want to go swimming in a lake - it's too deep! I was informed that Korean people like swimming in the ocean (where they can touch the bottom), but that a lake is much too deep. End of discussion.