Lake Ziway covers 424 sq km and reaches a maximum depth of 9 m. It is the largest of the lakes in the Upper Rift Valley.
This freshwater lake has five islands, some of which are home to only a few people. Tullu-Guddu is the largest and most populous. According to tradition, it is here, in a ruined church, that the Ark of the Covenant, accompanied by a large escort found refuge; indeed, the presence on the island of the small Zai community, speaking a Semitic original dialect close to the Tigre, may attest to this story. The shores of this lake, rich in fish, hosts abundant birdlife (swans, hammerkops, geese, osprey, egrets, ibis and sometimes even cranes); a significant colony of hippos is concentrated in the calmer coves close to fields in which towering plantigrades graze at night.