The Kakadu wetlands are the floodplains, billabongs, swamps and tidal flats of Kakadu National Park in Australia’s Northern Territory, about 171 km southeast of Darwin, where the East Alligator, West Alligator, South Alligator and Wildman rivers spill across the lowlands before reaching the Van Diemen Gulf. The park covers 19,804 km², and its wetlands are listed under the Ramsar Convention in two stages, Stage 1 on 12 June 1980 and Stage 2 on 15 September 1989, together about 13,760 km². The park is also a UNESCO World Heritage Site, first inscribed in 1981, and is jointly managed by its Aboriginal traditional owners and Parks Australia. Everything about these wetlands is set by one rhythm: a monsoon that drops most of a year’s rain between December and March, then almost none from May to September. The Bininj/Mungguy people divide that cycle into six seasons, and this guide follows them through one year.
Kunumeleng, mid-October to December: the build-up below the Arnhem Land escarpment
The water year begins at its lowest point. By October the floodplains are cracked clay, the billabongs are shrinking pools, and the air is at its hottest: Jabiru, the park’s main town, averages a daily maximum of 37.9 °C in October and has recorded 42.4 °C in November. The Bininj/Mungguy call this time Kunumeleng, the pre-monsoon storm season, when thunderheads build every afternoon over the sandstone of the Arnhem Land plateau.
That plateau is the wetlands’ water tower. Its escarpment rises to about 330 m above the plains and runs roughly 500 km along the park’s eastern edge and on into Arnhem Land. Around 140 million years ago much of Kakadu lay under a shallow sea, and the escarpment wall was a line of sea cliffs; the outliers, blocks of plateau since cut off by erosion, were islands in that sea. Today the plateau top is a harsh surface where water drains away quickly through chasms and gorges. Jabiru’s 1991–2020 averages give only 49 mm of rain in October, rising to 123 mm in November and 231 mm in December, enough to green the lowland woodland but not yet to fill the plains below.
For wildlife this is a lean, crowded season. Animals that spent the dry months around the last permanent water stay there until the rain arrives, and the frogs that sat out the drought buried in mud begin calling as the first puddles form. Kakadu has 25 frog species, and the northern bullfrog and the marbled frog are among the loudest once the swamps start to fill.
Kudjewk, January to March: the South Alligator and Magela floodplains go under
Kudjewk is the true monsoon. January and February each average about 370 mm at Jabiru and March another 297 mm, carried by monsoon troughs from Southeast Asia and, in some years, by tropical cyclones. Water pours off the plateau through gorges such as Jim Jim Creek, where Jim Jim Falls drops between 140 and 200 m into its plunge pool. In this season no vehicle can reach the falls by road, and they are best seen from the air.
Below the escarpment the creeks overflow onto the floodplains, and a few weeks of rain turn grassland into a sheet of shallow water that can stretch for kilometres. The rivers doing the work are short but heavy: the East Alligator, about 160 km long, drains 15,876 km² and carries an average of about 6,870 gigalitres a year to the Van Diemen Gulf, while the South Alligator, also about 160 km long, drains 11,917 km² and lies entirely within the park. Their floodwaters carry alluvial silt that resupplies nutrients across the plains each year, and they push fresh water out across the tidal flats, where the estuaries reach about 100 km inland.
A big wet can cut the park off. In the 2006–07 season, Jabiru’s heaviest on record, almost 2 m of rain fell in three months; the Arnhem Highway was closed for several weeks after floodwater badly damaged the bridge over the West Alligator River. The same water feeds an explosion of life. Kakadu has 53 recorded species of freshwater fish, 32 of them in the Magela Creek system alone, compared with 27 native species now left in the whole Murray–Darling system. Magpie geese, colonial breeders that gather in noisy flocks of up to a few thousand birds, are among the most conspicuous animals on the plains.
Bangkerreng in April: knock-’em-down storms and falling water
Rainfall at Jabiru drops to about 109 mm in April, and the floodwater begins to recede. Bininj/Mungguy call this Bangkerreng, the knock-’em-down storm season, after the violent, windy storms that flatten the tall spear grass that grew through the wet. The plains are still wet underfoot, but the creeks start to drop back into their channels and the first isolated waterholes appear as the sheet of water breaks apart.
This is the season when the floodplain plants show what kind of wetland Kakadu is. Spike rush and other sedges cover the open plains; freshwater mangrove, pandanus and paperbark trees of the genus Melaleuca line the channels; and blue, yellow and white snowflake water lilies float on the deeper pools. Nearer the coast, 39 of the Northern Territory’s 47 mangrove species grow along Kakadu’s estuaries, holding the muddy shore together and sheltering young barramundi.
Yekke, May to mid-June: patch-burning the lowland woodland
By May the trade winds have swung to the south and east, humidity falls, and May rainfall at Jabiru averages just 21 mm. The Bininj/Mungguy call this cooler, clearer season Yekke. Historically it was the time to start burning the woodland in patches to clean the country, clearing the dry grass early so that later fires would be smaller, and encouraging fresh growth for grazing animals. The larger mammals of these woodlands include agile wallabies, antilopine kangaroos, black wallaroos and dingoes.
The lowlands being burned are the largest part of the park, close to 70% of its area: gently rolling country of eucalypt woodland over shallow soils and ironstone, between the floodplains and the escarpment. In Yekke the wetlands and the woodland meet along a widening margin of drying mud. Around 11,246 km² of these savannas are listed by BirdLife International as the Kakadu Savanna Important Bird Area, for species including the endangered Gouldian finch and the red goshawk.
Wurrkeng, mid-June to mid-August: Yellow Water and the shrinking billabongs
Wurrkeng is the cold-weather season, with Jabiru’s average minimum falling to about 19 °C in July, although afternoons still reach about 32 °C. June, July and August together average only about 6 mm of rain. Most creeks stop flowing, and the floodplains dry out quickly, leaving water only in the billabongs, the deep backwaters and old channels that hold on through the dry.
Yellow Water, known in the local language as Ngurrungurrudjba, is the best known of these. As the plains around it dry, the birds and animals of a whole floodplain gather on the remaining water. Kakadu has recorded more than 280 bird species, about a third of Australia’s total, and the waterbirds concentrated in Wurrkeng include magpie geese, wandering whistling ducks, green pygmy geese, comb-crested jacanas, black-necked storks, brolgas and sarus cranes.
Dry-season concentration has shaped human use of the wetlands too. By the 1880s buffalo numbers were high enough for a commercial hide trade, which spread east from the Adelaide River to the Mary and Alligator Rivers. The shooters worked between June and September, when the feral water buffalo descended from animals released at the failed British outposts on the Cobourg Peninsula crowded around the billabongs. The buffalo did lasting damage to the floodplains, and introduced plants still do: para grass displaces the native food of many waterbirds, Mimosa pigra covers about 800 km² of the Top End, and salvinia has infested the Magela floodplain.
Kurrung, mid-August to mid-October: crocodiles crowd the last water
The final season of the water year is Kurrung, hot and dry, with ever-shrinking billabongs. Jabiru’s September average is under 14 mm of rain, while maximums climb back above 36 °C. Everything that needs water now shares very little of it, which is why fish, birds and their predators end the year packed into the same pools.
The top predator in those pools is the saltwater, or estuarine, crocodile, which can exceed 6 m. It lives alongside the smaller freshwater crocodile, which reaches about 3 m and is told apart by its narrow snout. Both were hunted for skins until the law caught up: freshwater crocodiles have been protected since 1964 and saltwater crocodiles since 1971. Swimming in billabongs is dangerous for this reason; in October 2002 a tourist was killed by a saltwater crocodile at Sandy Billabong.
Kurrung is also when the wetlands’ newer pressures show most clearly. Cane toads reached Kakadu’s wetlands in March 2001, and populations of goannas, northern quolls and many snakes crashed after native predators ate the poisonous toads. The Ranger uranium mine, surrounded by the park, stopped operating in January 2021, and the question of how to contain its low-level contaminated water through future wet seasons remains a management challenge. Within weeks of the end of Kurrung, the first Kunumeleng storms arrive over the escarpment and the cycle begins again.
Kakadu’s seasons are not tidy calendar months, and the Bininj/Mungguy names describe what the country is doing rather than a fixed date. For trip planning around them, see when to visit the Northern Territory; for the park as a whole, from rock art at Ubirr to the stone country, read our Kakadu National Park guide, and for the crocodiles, geese and wallabies that live across the Top End, our guide to Australia’s wildlife geography.