Conservation organizations have determined that the main threats to Nile crocodiles, in turn, are loss of habitat, pollution, hunting, and human activities such as accidental entanglement in fishing nets. Though the Nile crocodile has been hunted since ancient times, the advent of the readily available firearm made it much easier to kill these potentially dangerous reptiles. The species began to be hunted on a much larger scale from the 1940s to the 1960s, primarily for high-quality leather, although also for meat with its purported curative properties. The population was severely depleted, and the species faced extinction. National laws, and international trade regulations have resulted in a resurgence in many areas, and the species as a whole is no longer wholly threatened with extinction. The status of Nile crocodiles was variable based on the regional prosperity and extent of conserved wetlands by the 1970s. However, as is the case for many large animal species whether they are protected or not, persecution and poaching have continued apace and between the 1950s and 1980s, an estimated 3 million Nile crocodiles were slaughtered by humans for the leather trade. In Lake Sibaya, South Africa, it was determined that in the 21st century, persecution continues as the direct cause for the inability of Nile crocodiles to recover after the leather trade last century. Recovery for the species appears quite gradual and few areas have recovered to bear crocodile populations, i.e. largely insufficient to produce sustainable populations of young crocodiles, on par with times prior to the peak of leather trading. Crocodile 'protection programs' are artificial environments where crocodiles exist safely and without the threat of extermination from hunters.