Lake Hawassa lies to the west of the city of hawassa, The Hawassa basin is in an old caldera in the middle of the Ethiopian Rift Valley, between the Abijata–Shalla basin to the north and that of Lakes Abaya and Chamo to the south. The walls of the caldera form steep walls to the north and east of the basin while most of the flatter areas are intensively cultivated. Lake Hawassa is in the lowest portion of the caldera, along with a previously extensive wetland, Lake Shallo and the Shallo swamp. The swamp drains into Lake Hawassa through a small river called Tiqur Wuha, which means ‘black water’. There are no outlets from the lake, but water may seep away through the underlying volcanic ash and pumice. Hawassa is a freshwater lake, even though the system appears to be closed. The level of the lake varies considerably from year to year and a dyke has been built to prevent the town from flooding. The surface area ranges between 8,500 and 9,000 ha and the maximum depth is c.18–22 m. The shoreline varies between 50 and 65 km in length. Hawassa is the smallest of the Rift Valley lakes, but is highly productive. It has a rich phytoplankton (over 100 species have been identified) and zooplankton that support large populations of six fish species. The most important commercial species is Oreochromis niloticus, but there are also good populations of catfish and Barbus. The shoreline is gently sloping and mostly covered with vegetation that can extend 50 m or more into the lake. There are extensive beds of Cyperaceae and Typha spp. The dominant floating aquatic grass is Paspalidium geminatum, with other floating plants including Nymphaea coerulea, Pistia stratiotes and the smallest flowering plant in the world, Wolffia arrhiza. The lake supplies Awassa with all its water, and supports a thriving local fishery.
