I was casting a few years back and had a musky hit only about 10' from the boat and just under the surface. I got her in quick and popped the hooks easily, but when I released her she couldn't get below the surface. I was holding her tail until she swam off strong but she just stayed on top.
It was almost dark when I got her, and I used my flashlight and followed her with my troll motor for more than 2 hours until my battery died.
She appeared healthy and strong and was having no problems swimming, but after I couldn't follow her in the dark I decided there was nothing else I could do for her and just headed in.
I went back early the next morning and she was no where in sight, so hopefully she eventually got down deep and did OK.