Last year saw one of the biggest unexplained wildlife disasters to ever hit the Kruger National Park (KNP). Mass crocodile die-offs in the Olifants and Letaba rivers left staff, scientists and other experts searching for answers.Rangers and scientists in the Kruger National Park (KNP) have detected a cluster of crocodile mortalities mainly in the eastern parts of the Olifants and Letaba Rivers. More than 160 crocodile carcasses were found, but it is believed many more crocodile died and the carcasses simply washed away or were eaten. Post mortems on several recently dead crocodiles reveal that the deaths were caused by a condition called pansteatitis. This condition is caused by the depletion of antioxidants in the bodies of these animals. This depletion results in the hardening of the crocodile's fat reserves into a rubber-like mass, which is unavailable for normal metabolism. It is also extremely painful and the animal loses mobility. The crocodiles then either die of starvation or drown.A similar incident in Loskop Dam, in the Olifants River near Bronkhorstspruit, during 2007 was linked to a mass die-off of fish caused by sewage pollution that was followed by a blue-green algae bloom. The crocodiles feasted on the masses of dead fish, including the rotten fish with rancid fat. The cause of the Kruger die-offs remains a mystery. Pansteatitis is usually linked to mass fish die-offs, where the crocodiles are then exposed to rancid fish oils, which their bodies cannot break down. These rancid fish oils cause the oxidation seen in the crocodile's own fat. However, no mass die-off of fish have been observed in the Olifants River or the gorge itself and despite extensive investigations by SANParks, the department of water affairs, and numerous other independent research institutions no obvious causes or triggers to the outbreak could be found.What became apparent to all who took part in the investigation was the terrible state of the Olifants River and the need to do something about this. Conserving and protecting Kruger's river systems is proving to be one of the biggest challenges facing park managers, because unlike Kruger's animals which can be fenced in, Kruger's river systems aren't restricted by the Park's boundaries or even international borders. Whatever happens both up and down stream of the park, impacts on Kruger.Agricultural and industrial pollution, extensive irrigation and other impacts of human overuse and interference upstream and the recent completion of the Massingir Dam downstream have all contributed to making the Olifants Rivers one of the least healthy river systems in the whole of South Africa.At a scientific workshop experts agreed on the need for a holistic focus on the river system and adopted an umbrella project that will encompass many smaller studies looking at every aspect of the river system. From micro-invertebrates, to fish eating birds, sedimentation studies to human usage studies, "operation CROC" intends to build the bigger picture of what is really happening in the Olifants River. Since the first carcass was found, experts have tested water, sediment, crocodile and fish blood and tissue samples.In Kruger, to date, no direct fish die-off can be linked to this event. The scientific management and veterinary staff in Kruger will be monitoring these two river systems, as well as Kruger's other river systems, to monitor the extent of the problem and to attempt to identify the suspected environmental cause.