Seeing Stoat's post about being saved by his dog made me remember when the situation was reversed. Walking down the local marsh with my Lab/Collie cross years ago, he did the usual and dived into one of the field drains/ditches. They're about 8 feet wide at the bottom with 45 degree sloping sides, so wider at the top. Thin ice, no problem, he just swam in it but when I called him he seemed to have trouble getting to the sloping bank. Suddenly I realised something was wrong and he was in trouble.
I laid my gun down and thought about trying to get down the sloping muddy side to grab him but knew if I slipped I'd be in with him, so I started digging footholds in the bank with my knife while he thrashed about in the churned up muddy water. After what seemed ages I managed to get down almost to water level and grabbed first a front paw then his collar and heaved..
To my amazement as I dragged him out I saw a green plastic milk crate caught on both his back feet. Somehow his feet had got trapped, no doubt as he kicked close to the bottom of the drain. No wonder he was struggling to swim!
I untangled his feet and we both got up the bank. No injuries, both a bit cold and very muddy but a scary few moments because of a stray milk crate..