The Sewer Alligator is the main antagonist of the Johnny Test episode Johnny's Royal Flush.
When Johnny gets flushed down into the sewer he finds many things down there such as a water proof drill and a hungry alligator and that chases him. Meanwhile, Mary and Susan start tracking Johnny because he has a tracking chip inside him. When they fix the machine, they turn Dukey into a fish and flush him to go find Johnny. Dukey finds Johnny and the gator then Dukey starts slapping the gator in the snout with his tail and the two make a break for it.
Johnny and Dukey find an old taxi and hide in the trunk from the gator, in the trunk they meet new fish friends who were also chased by the alligator. The alligator breaks open the trunk as the fish swim to a disposer that is trying to suck them in. And to make it worse the alligator is infront of them. Johnny saw an opening on the top, and told everyone to swim up. There was a wall blocking them from the botanical garden. They try to jump over it, but the water pressure is too low. The alligator then follows them. Johnny then takes a risk by luring the alligator into the garbage disposer. The alligator catches Johnny in his mouth, but gets his snout into the snout disposer causing the water to rise. Johnny gets out with the water proof dental drill he found. They all then jump over the wall before the alligator gets torn to shreds.
- Despite him being an alligator, his appearance was more like a crocodile.
- The alligator on the title card is different from the one in the episode.
- The episode was hated by a lot of fans due to the alligator's dark gruesome off-screen death.