Teen Titans Season 1 Episode 8

When a mysterious amphibious villain called Trident makes off with a boatload of dangerous Toxic Waste, the Titans hop into the T-SUB and go on an undersea adventure to put a stop to Trident. This is Beast Boy’s big chance to morph into all sorts of undersea animals and show the team what a big hero he really is. But unfortunately another big hero shows up to steal the spotlight: a good-looking water-breathing teenage do-gooder named Aqualad.