Masters swimming offers some wonderful benefits such has the social and motivational aspects of a group, and a coach to give you structured workouts and occassional feedback. However, masters workouts have their downside for many swimmers!
If you do belong to a masters group, make sure you are not overdoing it. If your stroke technique is slipping because you are trying to “keep up,” if you are getting sick more often, feel too tired all the time, or facing burnout in the water, think about replacing at least some of your group workout days with technique-focused solo workouts, including lots of drills to keep your stroke on track.
There are many of this type of workout in The Complete Guide to Triathlon Swimming!