Just before the Umba flows into the Indian Ocean, it crosses the border to Kenya.

The mouth itself marks the most eastern point on the border between Tanzania and Kenya, which was largely made in a straight line to the northwest towards Lake Victoria in the 19th century.

On the upper reaches of the river in the mid-1960s rich deposits of precious stones, including sapphires and spessartine, were discovered.

The flow of the river has been observed over 40 years (1963–2003) in Mbuta, a town about 40 km above the mouth.

The average monthly flow of the river Umba hydrological station of Mbuta (in m3 / s ) (calculated using the data for a period of 30 years, 1954–84)[2]