The conservation situation is more grim in central and west Africa presumably for both the Nile and west African crocodiles. The crocodile population in this area is much more sparse, and has not been adequately surveyed. While the natural population in these areas may be lower due to a less-than-ideal environment and competition with sympatric slender-snouted and dwarf crocodiles, extirpation may be a serious threat in some of these areas. At some point in the 20th century, the Nile crocodile appeared to have been extirpated as a breeding species from Egypt, but has locally re-established in some areas such as the Aswan Dam. Additional factors are a loss of wetland habitats, which is addition to direct dredging, damming and irrigation by humans, has retracted in the east, south and north of the crocodile's range, possibly in correlation with global warming. Retraction of wetlands due both to direct habitat destruction by humans and environmental factor possibly related to global warming is perhaps linked to the extinction of Nile crocodiles in the last few centuries in Syria, Israel and Tunisia. In Lake St. Lucia, highly saline water has been pumped into the already brackish waters due to irrigation practices. Some deaths of crocodiles appeared to have been caused by these dangerous saline levels and this one-time stronghold for breeding crocodiles has experienced a major population decline. In yet another historic crocodile stronghold, the Olifants River, which flows through Kruger National Park, numerous crocodile deaths have been reported. These are officially due to unknown causes but analysis has indicated that environmental pollutants caused by humans, particularly the burgeoning coal industry, are the primary cause. Much of the contamination of crocodiles occurs when they consume rancid fish themselves killed by pollutants. Additional ecological surveys and establishing management programs are necessary to resolve these questions.