You have mentioned this Hadith as Sahih but certain Arab writers have explained it as weak (da’if). Can you mention any Sahih Hadith about swimming.
In the link provided above, two reliable Hadith masters who have authenticated this narration were quoted. That is quite sufficient to prove the reliability of this Hadith.
In fact, in addition to that, even the great commentator of Sahih Bukhari, Hafiz Ibn Hajar ‘Asqalani (rahimahullah) has declared this chain (of Nasai) as authentic (sahih).
(Al-Isabah, number: 1034)
One is more convinced by the rulings of these masters, especially when they are of the calibre of Hafiz Mundhiri and Ibn Hajar (rahimahumallah) rather than contemporary writers.
A word of Advice
I would like to caution you against shopping around for rulings, and rather stick to the views of one school, or else one would be easily confused, as is the case here.
And Allah Ta’ala Knows best,
Answered by: Moulana Muhammad Abasoomar