What’s the Difference Between Freshwater and Saltwater Crocodiles?

By Nat Hab Expedition Leader Matt Cornish

“That’s not a knife; this is a knife!” That right there is one of the most famous quotes in movie history from Crocodile Dundee, and it is one of the first things that comes to the mind of many travelers when they hear the words “crocodile” and “Australia.” Now, let’s put Paul Hogan and his barbecued shrimp aside for one moment and join us as we dive into the world of Australian crocodiles (metaphorically, of course).

In Australia, there are two different species of crocodiles: the endemic freshwater crocodile (Crocodylus johnstoni) and the largest species in the world, the famous saltwater crocodile (Crocodylus porosus). Firstly, their names are misleading, as both these species can inhabit freshwater and saltwater environments. However, as you will see below, they are very different.

Freshwater Crocodiles

Found throughout inland northern Australia, these reptiles can grow to a maximum of 13 feet in length and possess 72 razor-sharp teeth. However, they are not considered a threat to humans; these unique crocodiles primarily feed on invertebrates, fish and the occasional and unfortunate freshwater terrapin (small turtle). These animals have evolved to survive in a “Boom and Bust” ecosystem, with long dry periods followed by seasonal heavy rainfall events. When inland creeks and rivers begin drying, the freshwater crocodile is able to run across land in search of existing water bodies. Through millions of years of evolution, the freshwater crocodile has developed a physical adaptation: its hip structure allows it to gallop like a horse, reaching speeds of up to 12 miles per hour. Although unlikely, it is possible to see a crocodile running across a desert in Australia—now that would be a sight!

Saltwater Crocodiles 

Named the saltwater crocodile due to its ability to live long periods of time in marine environments, this animal can also successfully survive in freshwater environments, which may lead to confusion.

The saltwater crocodile is the longest and arguably the most dangerous crocodile species. These reptiles are native to northern Australia and live in Papua New Guinea, Indonesia, Malaysia, India and other Indo-Pacific nations. The most enormous saltwater crocodile officially recorded reached a length of 20 feet 3 inches and weighed almost 2,400 pounds, an animal equally impressive as it is terrifying. 

Boasting the most powerful bite in the world, saltwater crocodiles can produce over 3,500 pounds per square inch (PSI) in force, with a jaw length 1/7th of the animal’s total length. This provides saltwater crocodiles with a predatory weapon that can kill almost any unfortunate land-based animal. Considered one of the most successful coastal predators, saltwater crocodiles have mastered the art of ambush predation. 

Unlike many other reptiles, the saltwater crocodile boasts a very unusual four-chambered heart with fully conscious regulation. In other words, saltwater crocodiles can control the rate at which their heart beats and where that blood is pumped. This sophisticated mechanism allows crocodiles to hold their breath for up to seven hours and also prevents extreme blood loss during traumatic injuries. 

Crocodiles of Australia: Ancient Survivors

Fossil records in Australia suggest that modern-day crocodiles have remained relatively unchanged for more than 100 million years; they have truly reached evolutionary perfection. Given crocodiles’ extensive evolutionary history, their physical and behavioral adaptations are complex and impressive, but they are still relatively understudied.

Some of the most famous and downright eery footage of crocodiles is when they swim on the surface of a river and suddenly disappear with no ripple. So how do they do this? Osteoderms is the answer.

‘Oesto’ often refers to bony material, while ‘Derm’ refers to skin; therefore,’ osteoderm’ means bony skin. Crocodiles’ backs are covered with these large and often raised bony platelets inside the skin. These osteoderms extend down the backs of crocodiles, creating a streamlined structure that disperses water and prevents them from making ripples and splashes while sneaking up on their prey. 

Being reptiles, crocodiles also use external heat sources to regulate their body temperature. The osteoderms are covered in tiny holes through which blood flows. By basking in the sun, the osteoderms heat up, warming the crocodile’s blood and surrounding body. In easy-to-understand terms, the osteoderms work similarly to solar panels. They help warm the crocodile, which in turn helps produce energy and increase metabolism. 

Crocodile-Human Conflict

In Australia, the saltwater crocodile is the only croc species that could threaten a person’s life. But unlike in other countries, Australian residents do not rely on waterways for their livelihood (e.g., washing clothes, drinking water and operating poor-quality water vessels). Generally, the only reason people in Australia come in contact with saltwater crocodile habitat is while undertaking recreational activities such as swimming and kayaking.

Despite the very low number of fatal crocodile attacks in Australia (one per year), crocodiles are seen as a terrifying threat to human life. Subsequently, the Australian state governments are proactively removing wild crocodiles to lessen the risk of an attack. However, over the past decade, a more significant focus on crocodile education in Australia has proven to be the best way to mitigate crocodile-human conflict. 

Nat Hab’s Ultimate Australia Safari and Northern Australia Tour

So, where can we find these two Australian crocodile species?

In Australia, both crocodile species prefer warmer habitats. As such, they inhabit the northern half of the Australian continent. Saltwater crocodiles inhabit coastal areas, while freshwater crocs inhabit inland environments. 

Nat Hab’s Ultimate Australia Safari offers guests the opportunity to travel throughout Far North Queensland, where they will enjoy a boat cruise along the famous Daintree River. This is one of the best places to see saltwater crocodiles in Queensland. 

Our Australia North itinerary traverses some incredibly unique Australian bioregions, including Kakadu, Katherine and the Kimberley. On this adventure, travelers will have the opportunity to see wild freshwater crocodiles in the Katherine Gorge and areas of the Kimberley. Guests will also have the chance to spot saltwater crocodiles on an immersive boat cruise along Kakadu’s impressive East Alligator River.