To get the shallow zora glitch, all you have to do is dive in water deep enough to submerge human link but not deep enough to submerge zora link then put on the zora mask. The B button will then say Dive unless the water is really shallow. If the B button says dive, you can press B to get your feet off the ground. The water in southern swamp is normally too shallow to submerge Zora Link but not too shallow to make the B button say Dive after following those steps so after you press B, you can swim as a zora in the water in Southern swamp despite the fact that it's normally too shallow for you to.[1]