Wiktionary
like a duck takes to water
adv. (context simile English) Very naturally; without effort. alt. (context simile English) Very naturally; without effort.
Usage examples of "like a duck takes to water".
Once I got her straightened out, however, she had settled into being my administrative assistant like a duck takes to water, and the question of anything intimate developing between us never came up again.
You took to this business like a duck takes to water, though the land knows there ain't any too much water in these parts for ducks.