Part of the Semien Omo Zone, Mareka Gena was a triangle-shaped area located south of the confluence of the Omo River and its east-flowing tributary the Gojeb River, bordered on the southeast by Loma Bosa, on the west by Isara Tocha, and on the north by the Oromia Region.
Towns in Mareka Gena included Wacca and Weldehane.
Based on figures published by the Central Statistical Agency in 2005, this woreda has an estimated total population of 125,532, of whom 63,723 were men and 61,809 were women; 8,405 or 6.70% of its population are urban dwellers, which is less than the Zone average of 8.5%.
With an estimated area of 875.78 square kilometers, Mareka Gena has an estimated population density of 143.3 people per square kilometer, which is less than the Zone average of 156.5.
[2] Concerning religious beliefs, the 1994 census reported that 41.85% of the population said they observed traditional religions, 37.95% practiced Ethiopian Orthodox Christianity, and 19.44% were Protestants.