Varanus mertensi
Silhouette: Steven Traver · PhyloPic
In 3 days ~80% in a week >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 |
Likely
About 40% of wildlife watchers report a Mertens's Water Monitor sighting in Nitmiluk National Park on a given day, based on 13 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 3rd most-seen of the 13 reptiles we can rate there. Over three days the chance rises to about 80%, and over a week to over 90%, if each day is a fresh chance.
March
In that month about 60% of wildlife watchers report a Mertens's Water Monitor in Nitmiluk National Park on a given day, against about 10% in April, September and December, the lowest months.
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.
2nd of 3
Of the 3 parks where we can rate Mertens's Water Monitor sightings, Nitmiluk National Park ranks 2nd at about 40%. The best odds are in Litchfield National Park (Australia, about 80%).
GBIF citizen-science records
It is estimated from how often the Mertens's Water Monitor is recorded against all the reptiles logged in Nitmiluk National Park (13 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.
