Mertens' Water Monitor

Mertens’ water monitor is a semiaquatic species of monitor lizard native to northern Australia, most commonly found around freshwater habitats such as rivers, creeks, lagoons, and billabongs. With its streamlined body, long tail, and strong limbs, it is an excellent swimmer and has evolved to thrive both on land and in the water. The tail is laterally compressed, acting much like a rudder, and can be more than twice the length of the body. Their nostrils are positioned high on the snout to aid breathing while submerged, and their eyes are adapted for spotting prey both above and below the water surface.

 

Mertens’ water monitors are opportunistic predators with a broad diet, feeding on fish, frogs, crustaceans, aquatic insects, and carrion. They’re also known to eat birds and small mammals when the opportunity arises. Typically diurnal, they spend much of their day basking on rocks or logs near the water, always staying close to an escape route in case danger approaches. When startled, they will usually dive into the water and remain hidden beneath the surface.

 

Although relatively widespread, Mertens’ water monitors are facing increasing pressure from invasive species, particularly the toxic cane toad, which has caused significant declines in monitor populations across parts of its range. The lizards often attempt to eat the toads, which results in fatal poisoning.

 

Conservation efforts now focus on managing cane toad populations and monitoring vulnerable reptile species like the Mertens’ water monitor. These lizards play an important role in the health of their aquatic ecosystems by helping control prey populations and cleaning up carrion. Their presence in a waterway is often a sign of good environmental quality, and they are considered a key species in freshwater environments across northern Australia.

 

 

Did You Know?

 

Mertens’ water monitors can remain underwater for over 30 minutes at a time, thanks to their ability to slow their heart rate and reduce oxygen consumption while submerged.