Can Sharks Live in Freshwater?

Can Sharks Live in Freshwater?

The majority of sharks cannot live in freshwater due to several physiological reasons; however, a select few can spend some or most of their lives in freshwater.

This may come as a bit of a surprise, but you’re probably not going to find a shark in that pond or lake behind your summerhouse (disappointing, I know).

In fact, out of the nearly 1,150 species of sharks and rays (together known as elasmobranchs) currently recognized worldwide, only around 56 species (or 5%) are known to at least partially inhabit freshwater.

If you’re wondering why, you’re in luck because, in this article, we’ll not only be going over the physical features that restrict sharks to seawater but also give some examples of sharks that can thrive in freshwater.

Can Sharks Live in Lakes and Rivers?

A tiny percentage of sharks are able to live in freshwater, including lakes and rivers.

Unlike obligate freshwater species, which are confined to freshwater environments and consist exclusively of stingrays, sharks that can live in freshwater are known as euryhaline species due to their ability to survive in a range of salinities (the salt concentration in water).

A well-known example is the bull shark, which splits its time between salt and freshwater habitats.

Salinity and Buoyancy Prevents Sharks From Living in Freshwater

A number of physiological factors limit most sharks’ ability to live in freshwater. One reason is that most sharks cannot regulate their internal salt levels, which means that their bodies would have very little salt content in freshwater.

Having little salt in their bodies would be fatal because most sharks must maintain a certain concentration of salt so that their cells can retain their shape (without enough salt, their cells can rupture and cause bloating or death).

A second reason is that sharks do not have an efficient way of staying afloat in the water. Unlike other, more modern fish that have air bladders, sharks can only depend on their oily livers to stay afloat.

This means that whenever a shark enters freshwater (which has significantly less buoyancy than seawater), they must spend up to 50% more energy on the lift, plus their fatty livers can cause them to be much slower in freshwater than their saltwater counterparts.

Maintaining Equilibrium is Essential to Living in Freshwater

In a freshwater environment, euryhaline sharks are able to excrete urea and absorb any salt in the water via their gills, hence retaining equilibrium with the water.

Under normal conditions in seawater, they will retain the urea within their bodies while excreting salt through their rectal glands.

Despite this unique mechanism that allows sharks to live in freshwater, they are still limited by their inability to stay afloat unless they’re willing to expend excess energy, as seen by the well-documented bull shark.

Euryhaline Sharks are Present in Many Rivers and Lakes

Euryhaline sharks are found in a wide variety of river basins both at the tropical and sub-tropical levels.

These basins can be found up to several thousand kilometers upstream, thus demonstrating how far these species are willing to go to find freshwater (the reasons of which we’ll look at after).

They are very active in rivers and can easily travel between rivers and the sea due to their ability to survive in water of varying salinities.

Prey Availability and Mating Habits Influence Sharks to Travel

Euryhaline sharks might travel thousands of kilometers to freshwater lakes and rivers to feed or raise their young.

Some dolphin species, such as the Amazon River dolphin, live in freshwater environments, making them a preferable prey option for bull sharks.

The rivers can also be an optimal nursery area for raising their young, considering their lack of predators and relatively calmer waters compared to the sea.

3 Species of Sharks That Can Live in Freshwater

Now let’s take a look at 3 species of sharks that are relatively well documented and are known to spend part of their lives in freshwater:

  • Bull Shark
  • Speartooth Shark
  • Ganges Shark

Bull Shark

The bull shark is arguably the best-documented shark that’s known to spend at least part of its life in freshwater.

Growing to about 2.3 meters and weighing up to 130 kilograms, bull sharks have been observed swimming up to 2,500 miles (4,000 kilometers) up the Amazon River and live in Lake Nicaragua, located in South and Central America, respectively.

Thanks to their adaptive organs, bull sharks can survive up to 6 years in freshwater.

bull shark
Bull Shark
Albert Kok, CC BY-SA 3.0, via Wikimedia Commons

Speartooth Shark

The speartooth shark is a shark that is commonly found at the bottom of river floors in the Western Pacific areas such as northern Australia and New Guinea.

The largest known individual was found to be roughly 1.75 meters, although, based on jaw size, they were estimated to be able to grow to 2 or even 3 meters.

Due to accidental bycatch and recreational fishing, there are only an estimated 2,500 individuals left living in the wild. Hence, it is considered an endangered species and information on it is very scarce. 

speartooth shark
Speartooth shark
Bill Harrison from Wellington, New Zealand, CC BY 2.0, via Wikimedia Commons

Ganges Shark

The Ganges shark is very unique because, unlike the previously mentioned sharks on this list, the ganges shark spends its entire life in freshwater (exclusively in India).

They are about 178 cm in length, with an overall body shape resembling the bull shark (hence they are often confused with each other).

The Ganges shark, like the Speartooth shark, has also seen its population decline due to reasons such as overfishing and habitat degradation, eventually causing it to be considered critically endangered.

ganges shark
Ganges shark
Müller & Henle, Public domain, via Wikimedia Commons

Can Great White Sharks Live in Freshwater?

Unlike the bull shark, which has particular physiological adaptations that allow them to live in freshwater, great white sharks are not blessed with the same traits and thus, cannot live in freshwater.

If a great white shark were to enter and stay in a freshwater environment for long, the low amount of salt around them and the fact that the sharks cannot self-regulate their inner salt levels would mean that there is a risk of cell rupture and death due to the uneven concentrations of salt inside and outside of the cell.

Conclusion

Hopefully, this article has reassured you that it’s safe for you to go fishing in that pond behind your house and that you won’t accidentally hook onto a shark.

Although a small minority of sharks can be found in freshwater bodies, they are still restricted to large bodies of water connected to the ocean, so you certainly shouldn’t find a bull shark in your backyard pond anytime soon.