The Prayer of Signs (Salat al-Ayat) is performed when the following events take place: lunar eclipses and solar eclipses, even if they do not cause fear; and every celestial event that causes fear, like thunderbolts and black storms; similarly, during earthquakes as an obligatory precaution, as well as during every earthly event that causes fear, such as great destruction, landslides, etc.
It is not permissible for him to present himself to lead the congregational prayer if he knows that he does not fulfil the requirements of the Imam of the prayer, in such a way he would be considered as cheating them.If they asked him to lead the prayer, it is permissible to do so, although it is better not to in this particular case as well. If he was praying alone and someone decided to pray behind him in congregation, then his prayer is in order and he has not committed a sin. If he was not qualified to lead the prayer, he should not apply the laws of the congregational prayer on him, for example, referring to the people praying behind him when he has doubts.
Swimming for men, in itself, is permissible; however, these places are one of the reasons of falling into committing sins usually, unless the individual attends during the times when women do not attend.