He is going to go swimming对不对?为什么这样说?能说He is going to swim

对的,说的是他将要去去游泳|去钓鱼,go swimming固定词组.
swimming ['swimiŋ]
基本翻译
n.游泳
网络释义
Swimming:游泳|依靠自身推进力浮水而过的能力|游水
go swimming:去游泳|去钓鱼|游泳.
swimming cap:泳帽|游泳帽