The elements, along with the reluctance of pastoralist herders to leave their surviving cattle for higher ground, frustrated the delivery of the first overland relief supplies that reached the remote region.
Delays in the distribution of food, water, medicine and shelter raised fears that the death toll would rise in the devastated area.
At least 364 people were killed when the Omo River burst its banks on August 13, displacing about 10,000 from their homes and villages.
”Logistical nightmare”
"Our teams are still struggling to reach the affected areas, but the marsh and silt created by the floods are preventing us," said Petros Gebre, the deputy police chief of the Southern Nations, Nationalities and People's state.
"And, aid distribution is becoming problematic as about 3,000 people who have declined to be relocated are unreachable by land," he said.
The operations being handled by police and aid groups from the town of Jinka, about 800 kilometres southwest of Addis Ababa.
"We are providing them with aid drops of aid from helicopters but it's not clear how long we can do this," Deputy Chief Petros said, calling the situation a "logistical nightmare".
About 3,000 herders are refusing to leave the area despite assurances that the government would take care of their livestock.
Search teams have yet to recover an unknown number of bodies of drowned victims after villagers reported spotting them on the marshlands on the Omo River delta on Monday.
Floods caused by unusually heavy seasonal rains have battered huge portions of southern, eastern and northern Ethiopia since the beginning of the month.
At least 626 people have died in the deluge and at least 118,000 people have been left homeless.
UN appeal
Concerns about the spread of water-borne diseases are also growing as rain continues to pound the Ethiopian highlands.
The downpours have pushed water levels at least three critical dams to the breaking point, and authorities have begun controlled releases from one of the facilities, the Gilgel Gibe dam on the Omo River.
The United Nations has made an urgent appeal for US$5.82 million for the thousands who have been displaced as well as for the rehabilitation of infrastructure in the flood-hit eastern town of Dire Dawa, where 254 people were killed on August 6.
Forecasters have warned that six areas in the north, west and south of the country will likely face further flood threats from the rains that are expected to continue until the end of the wet season in September.