Tore a rotator cuff decades ago but it was my left so I never bothered to fix it.

Got tired of marathons and wanted more variety in my regime... so I slowly began increasing my laps at the pool until I could do a mile.

In actual tris I always finished the swim last (and was once almost drown when a swarm of Amazons swam right over the top of me)... but made up a lot on the bike and especially in the run.

It was a rewarding experience. I recommend it.

One warning. Swimming in open water is not the same as in a pool. Make sure you get in some practice in a lake.