Given its size and markings I would say you have a sub-adult female. They are magnificent lizards. And very wary. You can quietly approach to within about two or three metres and no further, and they will sit there watching you watching them. Come any closer and they dive in the water or disappear into a deep rock crevice or thick undergrowth. It requires quite a degree of stealth to sneak up on their blind side in order to have half a chance of getting hold of one. Mostly they do not try and bite when seized but the odd one will. Beautiful animals.
Blue