He approached the water tentatively as he tried to figure out just what the heck happened. Peering into the surf he began to see his friends surface from the water, they motioned and called to him to come into the water. It did seem inviting enough and he was less apprehensive now that he matched them in size. Besides, he felt dry, really dry. His neck burned and his skin itched and so he dove. He swam up to them with surprising speed even though they closed the gap quickly.
As he approached, something seemed different. Each of his friends did but he didn't pay much attention to it, he felt great to be in the water. One of them offered to race to unanimous agreement but then he saw it. They dove but rather than their previous human legs they had dolphin-like tails in various shades of brown, red, grey-green, blue-grey and, black. They'd become a pod of mermen. Just then he looked down at his legs to find that they were missing too, replaced by a blue-grey tail. His shock quickly faded into how natural it felt to be in the water. It felt so good... He probed his new form, it began at his thighs with his dick lying in a groove and just below it a small slit. The skin was smooth and soft but tougher than that of his upper body. Gill slits flicked on his neck and over his ribs. He dove and paid it no more attention as he traversed the depths with gentle flicks of his new tail, easily catching up to his new "pod".