Varanus mertensi
Silhouette: Steven Traver · PhyloPic
In 3 days >90%
Mertens' water monitor (Varanus mertensi) is a species of monitor lizard in the family Varanidae. The species is native to northern Australia, and is a wide-ranging, actively foraging, opportunistic predator of aquatic and riparian habitats. It is named after German herpetologist Robert Mertens.
Mertens' water monitor grows to a total length (tail included) of about 2.0 m (6.6 ft). It is dark brown to black above, with many cream to yellow spots. The underparts are paler – white to yellowish – with grey mottling on the throat and blue-grey bars on the chest. The tail is strongly compressed laterally, with a high median dorsal keel, and is about 1.5 times the length of head and body.
Amongst all monitor species, including even the water monitors of the subgenus Soterosaurus, Mertens' water monitor is morphologically the most well adapted to an aquatic lifestyle, being able to seal its upwards facing nostrils when underwater. It is capable of swallowing prey underwater, which is an ability not reported in any other monitor species other than the Borneo earless monitor (Lanthanotus borneensis). It is also the only monitor species reported capable of using its sense... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Litchfield National Park | 🇦🇺 Australia | |
| 2 | Nitmiluk National Park | 🇦🇺 Australia | |
| 3 | Kakadu National Park | 🇦🇺 Australia |
No species of the same family or order lives in Litchfield National Park, so these are its closest relatives here: other reptiles.
Very likely
About 80% of wildlife watchers report a Mertens's Water Monitor sighting in Litchfield National Park on a given day, based on 159 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the most-seen of the 24 reptiles we can rate there. Over three days the chance rises to over 90%, if each day is a fresh chance.
January, July–August and October–November
In those months about 90% of wildlife watchers report a Mertens's Water Monitor in Litchfield National Park on a given day, against about 70% in February, the lowest month.
Between noon and 3 pm
Across all the parks we cover, that three-hour window holds the most Mertens's Water Monitor sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
Yes
Of the 3 parks where we can rate Mertens's Water Monitor sightings, Litchfield National Park has the highest daily chance: about 80%. Next come Nitmiluk National Park (Australia, about 40%) and Kakadu National Park (Australia, about 30%).
GBIF citizen-science records
It is estimated from how often the Mertens's Water Monitor is recorded against all the reptiles logged in Litchfield National Park (159 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
