Swimming or floating in water whilst fasting
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Question: What is the ruling concerning swimming or floating in water whilst fasting?

Response: There is no problem in diving into water, floating or swimming because this is not from that which breaks the fast. The basis (for everything) is permissibility until (authenticated) evidences proves a prohibition or a disliking (for that). For this, there is no evidence indicating a prohibition or dislikeness. However, some people of knowledge dislike this out of fear that some water may reach the throat without (the person) feeling it.

Shaykh Ibn 'Uthaymeen
Fataawa Ramadhaan - Volume 2, Page 525, Fatwa No. 491;
Fiqh al-'Ibaadaat libni-'Uthaymeen - Page 191