In most of these cases the iguanas were still young and thus of a similar size to the water dragon. Often months after first writing to me about their success, these same people have written to me telling me that their iguana was acting aggressively towards their dragon and that they had to separate them. I have only heard of a few people who have successfully kept adults of both species together for an extended period of time. Iguana's like to pile on top of one another while basking. A large iguana could injure or accidentally suffocate a water dragon of any age if it were to lay on it for an extended period, not to mention the fact that iguana's do have sharp claws that combined with the weight of an iguana might cause the water dragon to be scratched when the iguana climbs on or over it.
Iguanas have large, powerful jaws equipped with serrated teeth.
If the iguana was in an aggressive mood it could seriously injure a water dragon by biting it. Iguana's are herbivores, water dragons are insectivores and or carnivores. I've heard of many iguanas that when housed with an insectivorous or carnivorous lizard began to eat the other lizards food items. They should be eating salads made up of a variety of vegetables, fruits, and greens. It is not okay, or even cute to see an iguana eating a pinky or chasing a cricket.