It is known for its aggressive nature, and presence mainly in warm, shallow brackish and freshwater systems including estuaries and (usually) lower reaches of rivers.

Their aggressive nature has led to ongoing shark-culling efforts near beaches to protect beachgoers, which is one of the causes of bull shark populations continuing to decrease.

[17] In early June 2012, off the coast of the Florida Keys near the western part of the Atlantic Ocean, a female believed to measure at least 2.4 m (8 ft) and 360–390 kg (800–850 lb) was caught by members of the R.J. Dunlap Marine Conservation Program.

[13][14] In the Arabian Sea, off the coast of Fujairah in the United Arab Emirates, a pregnant shark weighing 347.8 kg (767 lb) and measuring 3 m (10 ft) long was caught in February 2019,[18][19] followed by another specimen weighing about 350 kg (770 lb) and measuring about the same in length, in January 2020.

[22] The bull shark is commonly found worldwide in coastal areas of warm oceans, in rivers and lakes, and occasionally salt and freshwater streams if they are deep enough.

The bull shark has traveled 4,000 km (2,500 mi) up the Amazon River to Iquitos in Peru[28] and north Bolivia.

[2] It also lives in freshwater Lake Nicaragua, in the Ganges and Brahmaputra Rivers of West Bengal, and Assam in Eastern India and adjoining Bangladesh.

[citation needed] It can live in water with a high salt content as in St. Lucia Estuary in South Africa.

Bull sharks have been recorded in the Tigris River since at least 1924 as far upriver as Baghdad,[29] and has been rumored to also inhabit the Cahora Bassa lake upstream of the Zambezi.

Some skates (Rajidae), smooth dogfishes (Triakidae), and sandbar sharks (Carcharhinus plumbeus) regularly enter estuaries.

[citation needed] The bull shark is diadromous, meaning they can swim between salt and fresh water with ease,[40] as they are euryhaline fish—able to quickly adapt to a wide range of salinities.

[41] This bottleneck may have separated the bull shark from the rest of the Elasmobranchii subclass and favored the genes for an osmoregulatory system.

Elasmobranchs' ability to enter fresh water is limited because their blood is normally at least as salty (in terms of osmotic strength) as seawater through the accumulation of urea and trimethylamine oxide, but bull sharks living in fresh water show a significantly reduced concentration of urea within their blood.

This results in a large influx of water across the gills due to osmosis and loss of sodium and chloride from the shark's body.

All elasmobranchs have a rectal gland which functions in the excretion of excess salts accumulated as a consequence of living in seawater.

Bull sharks in freshwater environments decrease the salt-excretory activity of the rectal gland, thereby conserving sodium and chloride.

[43] The kidneys produce large amounts of dilute urine, but also play an important role in the active reabsorption of solutes into the blood.

[43] The gills of bull sharks are likely to be involved in the uptake of sodium and chloride from the surrounding fresh water,[44] whereas urea is produced in the liver as required with changes in environmental salinity.

[48] Bull sharks tagged inside the lake have later been caught in the open ocean (and vice versa), with some taking as few as seven to 11 days to complete the journey.

[48] A study of six bull sharks confined to a stagnant golf course lake in Brisbane, Australia, from 1996 to 2013 uncovered their adaptability to low-salinity environments, marking the longest recorded residency for the species under such conditions, and demonstrating their ability to live indefinitely in low-salinity aquatic environments.

[53] As part of their survival mechanism, bull sharks will regurgitate the food in their stomachs in order to escape from a predator.

This is a distraction tactic; if the predator moves to eat the regurgitated food the bull shark can use the opportunity to escape.

[60][11][15] The speculation that bull sharks may have been responsible is based on two fatal bites occurring in brackish and fresh water.

[61][27] In India, bull sharks swim up the Ganges, Bramaputra, Mahanadi, and other Indian rivers and have bitten bathers.

[64] This large movement of young bull sharks were found to be moving as a response rather than other external factors such as predators.

Threats to the bull shark are numerous, such as getting caught in fishing nets, overfishing for their oil, skin, and meat, pollution to their habitat, and more.

[67] In many areas of the world, including Australia and South Africa, there are shark-culling measures around beaches to prevent attacks on beach-goers.

One example is The Nature Conservancy satellite tagging sharks to track their migration and find their habitats in order to guide what areas require further protection projects.