I had lots of chickens for many years, and a few runner ducks for a few years. Free range at first, then in a run about the size of a tennis court, surrounded by poultry netting to keep them off the patio, and out of the vegetable plot (and out of the house). Kids aren’t good at avoiding treading in the copious amount of poo.
Ducks don’t NEED to swim, but they do need a deep enough water container to submerge their heads. My garden is level, on heavy clay soil, it doesn’t drain well. The ducks had a small rigid paddling pool, shallow enough for me to easily tip the water out.
The pool needed emptying and refilling at least once a day, but I could have done it every 15 minutes and it would still be filthy water being tipped onto the grass. Ducks love paddling through mud, and paddling not only their feet but digging their long bills through it. They poo in the pool, as well as all over the whole area they have access to. And in their house. Mine had hemp substrate (Aubiose) with straw on top, changed twice a week.
Tipping dirty water out of the pool and moving it to a clean, dry patch of grass swiftly meant that most of their run was more mud than grass. Leaving the pool in the same place, still tipping the dirty water onto the grass before rinsing and refilling with a hosepipe, meant the muddy fringe around the pool got wider and deeper and more unpleasant and difficult to extract my wellies. The ducks were so muddy by the time they got into the pool it immediately needed doing again, and they were so muddy by the time they made it over to some clean grass, they were desperate to wash it off... They’re ok with clean wet bills, feet and feathers but not dirty ones.
Chickens are brilliant about taking themselves to bed but ducks aren’t. They often had to be rounded up and shepherded into their house. Not always easy if you’re on your own. Not easy if you want to go away and someone else is trying to shut them in for the night.
Runners are prolific layers. I like duck eggs for baking cakes, and hard-boiling. The kids didn’t like them but I was always able to sell surplus eggs. Ducks seldom go broody.
Drakes can be a nightmare - one male to four or five females is plenty (and you don’t need a drake for the girls to lay eggs). It’s terribly stressful for the poor ducks if there are multiple drakes incessantly pinning them down to mate. Nothing in the way of sweet talk or romance, just wham-bam... on repeat.
Fox strikes are heartbreaking. Clearing up the carnage left behind is horrible. Now the land behind my place isn’t managed there’s too much cover for foxes and after losing the last three birds I called it a day. Miss them dreadfully, but I wouldn’t have ducks again without an established lake rather than just a garden pool.