As the name suggests, the Mertens' water monitor loves the water. During the day the monitor can be found basking on rocks and logs near the shoreline of rivers, creeks, billabongs and lagoons. The monitors are great swimmers and have a special valve in their nostrils that closes when they dive. Their nostrils are also on the top of their head, like a crocodile’s, so that they can stay partially submerged in the water when searching for prey. These big reptiles grow to a metre long and weigh up to 380 grams. They are light grey to dark brown, with a scattering of light yellow/cream spots. Their underbelly is light yellow to cream. When threatened, the Mertens' water monitor will typically slide into the water and hide under a rock or log.