Circular pond inside the Happy Valley Racecourse [c.1885-1890]
An article, The new 'Bowen Park', on page 2 of The China Mail, 1885-02-27, described Governor Bowen's visit to the racecourse to "turn the first sod", and start the project to drain and re-develop the land. Bowen said the project would "convert this marshy and malarious swamp on which we are now standing into a place of public resort." Based on this I've guessed 1885 as the date the pond was dug, but corrections welcome!
We've got a better idea of when it was filled in again.
After the Hong Kong Golf Club was founded in 1889, their first golf course was laid out here, on the flat land inside the racecourse. However, that large pond caused problems for the golfers: "One hole, the 8th, became known as 'Old Misery' on account of the pond which swallowed up balls, scarce at the time." See page 181 of The Encyclopedia of golf
I'm guessing the golfers included a few members of government, as they soon had the pond filled in: "Prior to 1890 there was a large round pond, at the northern end of the land inclosed [sic.] by the race-course track, which was filled up in that year for the convenience of golfers, who started the first Hongkong Golf Club there in 1889 (now known as the Royal Hong Kong Golf Club)." See page 355 of Old Hongkong by Colonial