I wrote here, and again here, about Americans’ use of the typically BrE “sport,” rather than the traditionally American “sports.” I’ve continued to see a lot of examples, most recently from tennis star Venus Williams yesterday at the Australian Open:
I think why people love sport so much is because you see everything in a line. In that moment, there is no do-over. There’s no retake. There is no voice-over. It’s triumph and disaster witnessed in real time. This is why people live and die for sport, because you can’t fake it.
At this point, AmE “sport” seems sufficiently widespread not to warrant further comment.
notoneoffbritishisms.com 
Yet when the activity is aquatic, BrE generally uses the plural form preceded by “water”.
I don’t know that sport is typically British and not typically American. The American song about A White Sport Coat and A Pink Carnation is what we commonly call a sports jacket. Aristocrats and Savile Row tailors might call it a sports coat. We also talk about a sports reporter, a sports venue, sports stadium, school or village sports day and many similar instances. We do also talk about sport as a collective similar to how we’d refer to science. We’d also talk about sciences in some contexts. Do you watch sport? We might answer that we do watch sport, some sport or some sports, indicating either sport as a totality, a certain amount or certain sports.
I agree. For example, it’s always “winter sports” not “winter sport”. But there’s “motorsport”, not “motorsports”.
The British Sub Aqua Club has a grade called “Sports Diver”, but the American PADI has a magazine called “Sport Diver”. There doesn’t seem to be any consistency.
Yes, Sammy, but Americans refer to the collective enterprise as “sports,” as the British do not. The sports pages. “I like sports.” Sports reporter. ESPN is a sports channel. Etc.
Could Ms WIlliams have used the Australian idiom because she was in Australia and had picked it up by hearing it being used by Australians?
Quite possible.
She’s been to Wimbledon and the Aussie Open lots of times so it’s not likely to be just from this occasion.
Ben, you wrote: >> but Americans refer to the collective enterprise as “sports,” as the British do not. The sports pages. “I like sports.” Sports reporter. ESPN is a sports channel. Etc. <<
I think it's rather more subtle than that! "The sports pages", "He's a sports reporter", "BT Sport is a sports channel": these are all perfectly natural-sounding British English phrases, indeed they are THE idiomatic way of expressing the notions involved.
It's the last example ("BT Sport is a sports channel") which provides the key. In BrE the mass noun "sport" (e.g. "sport is a business") becomes "sports" when used adjectivally — thus:
"I used to play a lot of sport", but "We train at the sports centre"
One of the longest-running BBC radio programmes is "Sports Report", which has been broadcast every Saturday afternoon since 3 January 1948, and there were other programmes with titles like "Weekly Sports Review" as early as 1924 — but also "Sport and Sportsmen". That contrast between "sports" (in compounds) and plain "sport" elsewhere is also shown by the fact that items within "Sports Report" have included the likes of "Talking Sport", "Sports Round-up", "Sport in the Midlands", "Sports Quiz", etc.