Columbia River In-Lieu and Treaty Fishing Access Sites Improvement Act (Sec. 2) This bill authorizes the Bureau of Indian Affairs (BIA) to assess sanitation and safety conditions on land set aside to provide Columbia River Treaty tribes access to traditional fishing grounds. The bill applies to land held by the United States for the benefit of the Nez Perce Tribe, the Confederated Tribes of Umatilla Indian Reservation, the Confederated Tribes of the Warm Springs Reservation of Oregon, and the Confederated Tribes and Bands of the Yakama Nation. The BIA may enter into contracts with tribes or tribal organizations to improve sanitation, safety conditions, and access to electricity, sewer, and water infrastructure on this land. (Sec. 3) The Government Accountability Office must evaluate whether the sanitation and safety conditions on the lands have improved as a result of the contracts and report on the results of the evaluation.