"Drowning doesn't look like drowning" and statistics that show more than 50% of children drown within 25 yards of a parent or guardian are very sobering statistics. So it is time to put some risk prevention in place - pull up a cup of coffee and read the attached article (investment: only 3 minutes).
I can illustrate this with a story from a friend. Five adults were by the pool where eight children were playing - only problem is that the adults were busy chatting. My friend's son was about six years old at the time and a competent swimmer, but he hit his head on the edge of the pool as he dived in, and although he wasn't knocked out he was shocked, and underwater. He took a big gulp of water and started to drown. The adults looked around to see him floating face down in the water. They scooped him, out tipped the water out, and performed the kiss of life while an ambulance was called - he started to breath and before he had completed the trip to hospital was asking for food.
Share the story with your kids as a reminder to keep an eye out for each other as well.