Lake Nakuru is a very shallow, highly alkaline lake with surrounding forests and grasslands fed by four seasonal rivers and the perennial Ngosur River. A range of ecosystems including sedge swamps, seasonally flooded and dry grasslands, floodplain forests and various types of scrubland support some globally threatened mammal species such as the critically endangered African black rhinoceros (Diceros bicornis) and the vulnerable common hippopotamus (Hippopotamus amphibius), and regionally threatened bird species such as the African darter (Anhinga rufa) and the great egret (Ardea alba). The Site supports a large population of lesser flamingo (Phoeniconaias minor). The introduction of the fish species Magadi tilapia (Oreochromis grahami ) in the Lake in the 1960s attracted some other secondary consumers, including several fish-eating bird species. There has also been an accidental introduction of the Nile tilapia (Oreochromis nilotica) that increased numbers of freshwater piscivorous bird species. Tourism is the main activity within the Site and attracts over 300,000 national and foreign vacationers annually. Threats within the park include invasive plant species and fencing that prevents animal migration, while threats within the Lake’s catchment include the expansion of Nakuru town, forestry and agricultural activities that degrade water quality and increase erosion and sedimentation.