Does he know how to get in the water? I bought a kiddy pool for my ducks to swim in and my favourite Daffy, just ran around the edges looking for a place to get in, so I picked her up and put her in, and she is still the most trusting of being picked up. So maybe if you move your duck closer to the the water, just so it touches his feet he may try and do it himself nex time.
Would loooover to see a pic. I'm still on the thread "Muscovy keeper share your pic!" heh heh, reading it in bed, gunna take me a while, got like 10 tabs open. Sorry, rambeling.