A Code of Practice For Muslims in the West:
Youth's issues » General Rules
Ayatullah al Uzama Syed Ali al-Husaini Seestani
500. It is not permissible for a Muslim man to go to unisex swimming pools and other places where people go about half-naked. That is if it entails a harãm act. Based on obligatory precaution, one must refrain from going to such places, even if it does not entail a harãm act.