E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Swim (In the).
In society. The upper crust of society. An anglers phrase. A lot of fish gathered together is called a swim, and when an angler can pitch his hook in such a place he is said to be in a good swim. To know persons in the swim is to know society folk, who always congregate together.
1
Cottontree, who knows nearly everybody in the swim of European society informs him that Lucy Annerley is the daughter of Sir Jonas Stevens.A. C. Gunter: Mr. Potter of Texas, book iii. chap. xiv.