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Merten's water monitors, several of which live at the Australia Zoo, are perhaps the most amphibious members of the monitor family.

In the wild, they are typically found near rivers, large creeks, lagoons, reservoirs and billabongs in northern Australia.

Well adapted to an aquatic life, Merten's water monitors are terrific swimmers. They are able to hold their breath for several minutes at a time, and their nostrils are equipped with a special valve that shuts tightly when they dive underwater.

These monitors spend much of their day basking on riverbanks or on exposed rocks and logs close to the water. When threatened they almost invariably slide into the water and swim away, seeking shelter beneath submerged rocks, overhanging banks and other well-concealed places.

They have nostrils on top of their head, which allow them to stalk prey from a partially submerged position like an alligator or crocodile. They can also walk underwater, their eyes wide open, scanning the depths for potential prey. However, most hunting involves active swimming.

As one would expect, Merten's water monitors take most of their food from the water. Crabs are a favorite, as well as frogs, fish, shrimp, crayfish and other small crustaceans. They will also take land-based prey on occasion, such as birds, small mammals, reptile eggs and insects.

In captivity they are fed a range of pinky rats, fish, insects and yabbies.

Merten's water monitors generally breed during the dry season, with males engaging in ritual combat for mating rights.

Expectant females lay their eggs in a meticulously built nesting chamber at the end of a burrow, sometimes depositing leaf litter with the eggs before sealing the lair. The eggs, usually about nine of them, hatch between six and nine months later.