I used to study (for my sports science degree) with a number of guys, elite swimers (competing in worlds, European championships and Olimpic games)
I know that those who competed in BREAST STROKE did quite a bit of weight training.
The guy that did back stroke did some too.
the other free stylers did not!
yep, agree, they did quite a lot work with extra hand pads for increased water resistance, and pulled some shit behind them in water when they were swimming.
Even those that did, I would not say now that they did anything fantastic at that time.
However, from my perspecive now as a S&C Coach, I reckon that some basic lifting would not hurt any swimmer!!!
Some squats, overHead squats, power cleans, snatches, deadlifts, rows, chins, good abs work (with hanging legs/knees raises) will definetely make you a stronger athlete and this is to say a stronger swimmer.
I have not met anybody yet who complained on excesive amount of strengh he had!!
(well, apart from my mumm when I was supposed to twist close tight her jars with pickles - but I guess, it does not count here!)
P.S. 3 session a week, good bodyweight warm-up, 4-5 basic exercises, 5-6 reps, always at the end some external arm rotator combo (arm abducted and adducted superset) - and make it light but, rather hight volume to balance out internal rotators that work so intensively while swiming.
finish wih some extra stretch