Kalmius

Kalmius, Кальміус
Kalmius river
Origin	Donetsk Oblast, Ukraine
Mouth	Azov Sea (Mariupol)
Basin countries	Ukraine
Length	209 km
Basin area	5,070 km²

The Kalmius (Ukrainian: Кальміус) is one of two rivers flowing through the Ukrainian city of Mariupol. The other river called the Kalchik flows into the Kalmius. The Kalmius flows into the Sea of Azov near the Azovstal steel manufacturing complex in Mariupol.

Kalmius was the name of a 16th-century Cossack encampment where the city of Mariupol was later founded.

The Kalmius Trail was a Tatar raiding trail, one of the branches of the Muravsky Trail.

After an offensive by the separatist forces of the Donetsk People's Republic in August 2014 during the War in Donbass, in southern Donetsk Oblast the river became the boundary between Donetsk People's Republic-controlled territory on the east bank of the river, and Ukrainian government-controlled territory on the west bank. A Donetsk People's Republic unit was named "Kalmius" Battalion.