Note: It seems necessary to actually step into the water (mounted, or on foot) to spawn Grokkluz. If he does not spawn, have patience and try again in a few minutes. Approach the gator to make him attackable and able to be leashed.
Defilers should remove Abominus (walking under water) or he may not spawn.
If you choose to fight Grokkluz for AA, note that he has a respawn timer of ~5 minutes and will decrease Clan Grobb faction by 100 points (and, oddly enough, increase Clan Brokenskull faction by 50 points).