Found dead at the scene were 31 women, 11 children and six men, many of whom had been hacked to death, or had been barricaded in their huts and burned to death. Four others died at a hospital.
Tensions over land between pastoralists and farmers in isolated rural communities go back centuries in Africa and persist in Kenya. In many countries, particularly in the Sahel region and the Horn of Africa, the problem is often exacerbated by government neglect.
An undercurrent in the Darfur conflict in western Sudan was long-running tensions over land use. In central Nigeria, clashes between nomadic herders and farmers sometimes leave dozens dead. Ready access to guns across the region has worsened the toll of tribal clashes.
Police said Wednesday's clashes between the Pokomo and Orma people in the Tana Delta region grew out of long-standing disputes over the use of grazing land and water.
"They were armed with crude weapons: machetes, bows and arrows and spears. Some had guns," area deputy police chief Robert Kitur told Reuters by telephone. Forty-eight died at the scene and four others died in the hospital, Kenya's Standard newspaper reported. Many others were injured.
Kitur told the Standard that dozens of armed men from the majority Pokomo tribe, whose members cultivate land on the Tana River flood plain, attacked the minority Ormas, pastoralists who rely on cattle herding to survive.
Police characterized it as an attack in revenge for an Orma assault on a Pokomo village that killed three people last week. Local news reports said tensions also had flared because cattle owned by Ormas destroyed Pokomo crops.
There have been similar outbreaks of ethnic violence in Kenya's north in recent weeks.
-- Robyn Dixon