The Picture of London, for 1803 (1802)
The annual Picture of London would tell tales of sailing and rowing competitions on the Thames in the summer. The Sporting Magazine (1815) tells us of two such events for that July:
Vauxhall would host similar events:
This article (https://www.lassco.co.uk/lassco-news/2019/05/13/the-vauxhall-grand-regatta/) recaps the Georgian tradition of the Vauxhall Sailing Regatta and subsequently the match that would march into the early years of the 19th Century.
The professional watermen that provided ferry and taxi services on the Thames in London were part of some of the first modern rowing races in the summer, which would attract large crowds to watch the skilled matches sponsored by the guilds, livery companies or wealthy riverside home owners. Doggett’s Coat and Badge was the oldest known rowing race between up to six apprentice watermen. The race has been held annually since 1715 (Doggett’s Coat and Badge – Wikipedia).
In the Regency romance world, we tend to think of London as thin of company in the summer, but it was as bustling with activity as a warm summer’s day in London today (well, maybe not as many people, but you get the idea).