MERTENS WATER MONITOR Varanus mertensi Glauert, 1951
This lizard attains 1.2 metres in length. it is found throughout tropical and adjacent parts of Northern Australia except for eastern Cape York. Populations in some areas have been devastated by the newly introduced Cane Toad Bufo marinus.
The Mertens Water Monitor lives around rivers, lagoons and large creeks, into which it will retreat when threatened. It will often dive into the water and swim away, hiding under submerged rocks, overhanging banks and other well-concealed places. The Mertens Water Monitor can also remain submerged, with only its nostrils protruding above the water surface, if necessary. This lizard is carnivorous and feeds on available frogs, smaller reptiles, fish, etc. This lizard is known to walk along river bottoms, in a manner not unlike other monitors on land.
About nine eggs are laid in a carefully constructed nesting chamber at the end of a burrow. Leaf litter may be deposited with the eggs by the female, who then seals the burrow and nesting chamber. The eggs hatch between six and nine months later.

The above was from the book Australian Reptiles and Frogs by Raymond Hoser and now available on a fantastic CD-Rom along with a vast amount of other information, papers and the like on reptiles, frogs and other wildlife.