It can happen quickly. I was with my wife and kids
at a local lake when my wife went into the water beside the dock in about 7' of water. I was about 30' from her and as it was summertime and warm, I was not too concerned as all she had to do was to move herself along the dock a short distance to shallower water and walk out.
She had already removed her PFD
before she fell in and so was not wearing one. As I looked toward her and was starting to go over and help her I realized that there was far more wrong here than just being wet.
She had grabbed the side of the dock to try to pull herself up onto the dock and not having that much upper body strength, she realized that she could not do so. She had started to pull herself along the dock toward shallow water and tired very quickly in the cold water and full clothing
. She was unaware of the water depth
as you could not see the bottom there, she only knew that it was over her head
and as she was trying to pull herself along her legs were swinging under the floating dock.
By the time I was able to get the small boat to her and get ahold of her to help her to shallow water, she was exhausted and terrified.
I will never forget the look of desperation and terror in her eyes...
This experience changed some of our rules about wearing pfd's even when on a dock for the adults in our family, and have always been that way for our kids