Question:
Is it assur for an older lady fully dressed with SHVIM KLEIDER to go swimming with older non jewish and irreligious jewish men?
Answer:
It is incorrect (and according to some poskim assur) for her to go to a mixed swimming pool even when she is fully dressed. The poskim say that it is a lack of tznius for her to look at the men, and to be in such a place, there is also an issue of maris ayin for her to be in such a place.
Sources:
Rivivos Efrayim 2-197(25), Yabia Omer 1-pg. 20. Halichos Bas Yisroel 7-17.