Reference: Fataawa Ramadhaan – Volume 2, Page 524, Fatwa No.490
Fataawa Ibn ‘Uthaymeen – Volume 1, Pages 509-510
Question: What is the ruling regarding swimming in the sea or in the pool during the day in Ramadhaan?
Response: We say [that] there is no harm in the fasting person swimming in the sea or in the pool, whether the pool is deep or otherwise, he can swim as he wishes and immerse himself in the water. However, he must – to the best of his ability – take care not to allow any water into his stomach.
Swimming energises the fasting person and assists him in his fast; And that which energises [a person] in obedience to Allaah, then there is no harm in it because it is from that which reduces the effects of hardship of worship for the worshiper and makes it easy for him.
Allaah (Tabaarak wa Ta’aala) says in the verses related to fasting:
And the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
So there is no harm in swimming in the pool, just as there is no harm in taking a shower and other than that; And Allaah has the Complete Knowledge [of all affairs].