The rivers of northern Australia are subject to tropical wet and dry seasons, providing a regularly changing habitat for a unique and diverse group of animals.

From November to April, the flat coastal plains are flooded by monsoon rains, but for the rest of the year very little rain falls, and the upper reaches of some rivers run completely dry. During the wet season the swollen rivers are almost entirely fresh water, but as flood waters recede in the dry season, salt water travels upstream as far as 100 kilometres from the coast.

Most fish and other animals living in this environment are well adapted to the fluctuating salinity. Two good examples of such salt adapted animals on display in the aquarium are the Barramundi, a large fish highly prized for both food and sport, and Australia's largest predator the Saltwater or Indopacific Crocodile, which is also the largest reptile in the world.

Some northern species are less salt water tolerant and so take sanctuary in fresh water found in the far upper reaches of larger, permanent rivers. The lungfish and saratoga on display at the aquarium are two such species. What these fish also have in common is that their nearest ancestors are found in South America and Africa, indicating that the ancestors of these fish have been around since Australia was part of the giant supercontinent called Gondwana, around 140 million years ago.

Quick Facts

The rivers of the Far North face a number of environmental threats:

• Mining activities cause sedimentation and the introduction of heavy metals. 
• Introduced species of fish and plants compete with native species for food, light, oxygen and space.