Local features include the Kesubo Swamp to the north and the Siracho Escarpment to the east, both within the National Reserve. The reserve is also famous for its geysers and hot springs. The lake waters are of Na-HCO3-CO3 composition. They originate from inflow from the Sandai and Emsos rivers, and from about 200 alkaline hot springs that are present at three onshore sites: Loburu, Chemurkeu, and a southern group (Ng'wasis, Koibobei, Losaramat). Other springs discharge directly from the lake floor. Lake Bogoria also contains the highest concentration of true geysers in Africa (at least 18 are known). The lake waters are alkaline (pH:10.5) and saline (up to 100 g/L Total Dissolved Salts). The lake has no surface outlet so the water becomes saline mainly through evaporation, which is high in this semi-arid region. The lake itself is meromictic (stratified) with less dense surface waters lying on a denser more saline bottom waters. Although hypersaline, the lake is highly productive with abundant cyanobacteria (Arthrospira fusiformis) that feed the flamingoes, but few other organisms inhabit the lake.