The phrase like a duck takes to water, and its variants, mean: easily, readily.

This phrase occurs, for example, in the following from Opportunity clicks, by Derek Smith, published in The Stage (London, England) of Thursday 27^th October 2005 [page 23, column 1]:

Advances in technology […] have meant that today’s actors look for work through methods unrecognisable to their predecessors. They must be scam-aware but going online to get work is increasingly the way to go.
As with most good ballets, the recent leaps and bounds in IT technology have been highly impressive. Just as laudable has been the way that the acting profession—sometimes inaccurately caricatured as old-school and dated—has embraced those fast-moving changes. Young drama students, of course, take to the wonders of the worldwide web like ducks to water but so too have older performers.

The earliest occurrences that I have found of the phrase like a duck takes to water and variants are as follows, in chronological order:

1-: From a review of The Beggar’s Opera, by John Gay (1685-1732), produced at the Theatre Royal—review published in The Edinburgh Dramatic Review (Edinburgh, Midlothian, Scotland) of Wednesday 22^nd June 1825 [page 698]:

Stanley’s Filch is the true gallows cove, the one who seems to have come into the world with a certain philosopher’s maxim impressed as an instinct upon his mind, that the world is a forest of wild beasts, in which each may justifiably prey upon the others. He takes as naturally to thieving as a brood of ducks take to the water; and appears as unconscious as they do that he is acting amiss.

2-: From Popular political economy. Four lectures delivered at the London Mechanics’ Institution (London: Printed for Charles Tait and William Tait, 1827), by the British political economist Thomas Hodgskin (1787-1869) [Introduction: page 25]:

The division of labour among individuals, and the wonderful co-operation of different classes of labourers to produce a common result, by which the productive power of the whole is amazingly increased, are not the result of human or legislative wisdom, foreseeing and willing the sublime, and for us most important, effect of general opulence, but of an instinct in man, by which he takes to this peculiar practice, as a duck takes to the water and a fox to his cave.

3-: From The Newspaper Office, published in The Albion (London, England) of Wednesday 2^nd February 1831 [page 1, column 4]—reprinted from Whittaker’s Monthly Magazine:

“Editor.—Why, to tell you the truth, I——
“Member.—Aye, out with it, let me hear the truth, if only by way of novelty. Truth indeed! as if an editor ever knew what it was! Why, Sir, a duck takes to the water, a leech to a horsepond, an alderman to a turtle-feast, or a placeman to a sinecure, with infinitely less alacrity than an editor to a falsehood.

4-: From Juvenile Transportation. Point Puer, Van Dieman’s Land, published in The Mirror of Literature, Amusement, and Instruction (London, England) of Saturday 17^th October 1835 [page 250, column 1]—the following is about “children in the lower neighbourhood of London”:

These boys go to crime as naturally as a duck takes to the water—it is their element.

5-: From Japhet, in Search of a Father, by the British novelist Frederick Marryat (1792-1848)—as published in the United States Telegraph (Washington, District of Columbia, USA) of Saturday 7^th November 1835 [page 1, column 5]:

“My father, as you may not perhaps be aware, was highly connected, and all the family have been brought up to the army; the question of profession has never been mooted by us, and every Talbot has turned a soldier as naturally as a young duck takes to the water.”

6-: From Musings of an Unreformed Peer, in Poet’s Corner, published in the Chester Chronicle, and Cheshire and North Wales Advertiser (Chester, Cheshire, England) of Friday 15^th July 1836 [page 4, column 1]:

Like ducklings, to water instinctively taking,
So we, with like quackery, take to law making.