I can't tread water

I can't float well

I can swim, but once I stop, if I can't stand, I'm done for

man look at animals... just do the doggy paddle. it's the most natural treading water move for any amateur.
floating is really about relaxing so you not fighting to sink. practise somewhere safe
both these things could save your life and they easy to learn with some practise.
swimming is a lot of cardio and most especially when you going against a current not pool. a lot of people get frantic and drown because they splashed around and wasted as much energy as running a sprint, get tired and go down. minimize your energy loss, do simple exercises and just learn to chill in the water longer and longer and your confidence will build up.