Knowing your water predators would be helpful; what region and what sort of lake, private or public? Can you get approval to fence into the lake? Do you want to fence out snapping turtles, otters, egg eating snakes, ect. . ? Do eagles frequent the lake? General guidelines include having brush cleared back so sneaky 'coon, foxes, and bobcats don't have an easy approach while still having bushes and/or willows for your duckies to escape from birds of prey. Hope you have some time and $$ resources as living on a lake would be bees knees for pet ducks
To quote Kathiquacks, "Also, make sure your ducks know to return to the coop at night - I’ve had days my ducks didn’t want to return from the lake, and it was rather stressful not being able to get them back : hmm For this, I recommend only having their feed in or near the coop." If your ducks have only a kiddie pool now, most ducks are passionate about a natural body of water. At sunset, they'll snicker at you and stay 20 ft out even if hungry, owls have plucked off their sisters from beside of 'em, and alligators are sleuthing about. Get them into a comfortable habit of going in to your coop around sunset.
Nice drawing, draw us another and do tell what you learn in your new setup.