By October the humidity is building up for the next Wet season. In the Wet huge waterfalls drop from the surrounding Arnhem plateau into the national park. The South Alligator River and other rivers in the park flood.
Gravel roads become impassable.
As the rivers spill over onto flood plains the lower reaches of the rivers become a huge wetland with prolific bird life. The grass rapidly grows two metres tall. Boat cruises on the Yellow Waters wetlands is the highland of Kakadu National Park. In the dry the rivers recede leaving only waterholes in places, sometimes known in Australia as billabongs. The waterbirds concentrate around the little remaining water until the next Wet season when they disperse.