The folowing is from poster “otr” in this thread here http://www.theyeshivaworld.com/coffeeroom/topic/lo-taturu-and-women
????? ?????? ????? ?”? – “??? ????? ???? ???? ????? ???? ?????
????? ?? ?? ???? ???? ???? ?? ????? ???? ????? ???”
??? ?????? ???? ??”? “??? ??? ???? ????? ??? ????? ????? ???????
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Basically, the issur of histaklus does not just apply to men, it also applies to women.
Posters also kept mentioning that there’s a Shevet HaLevi that holds Lo Sassuru also applies to women (though I’m not sure where).
Also, there’s a Sefer Chinuch that says Lo Sassuru is a generic issur to not do or think of anything Ta’avadik. http://www.hebrewbooks.org/pdfpager.aspx?req=37518&st=&pgnum=48
Being that there can be an issur de’oraysa of histaklus for women to look at other men, I would be careful to not mattir looking at men at the pool, and there may even be an issur of Lifnei Iver for the men.
Disclaimer: I am not a posek. At all.