The Mohelka is a river in the Czech Republic, a right tributary of the Jizera River. It flows through the Liberec and Central Bohemian regions. It is 41.6 km (25.8 mi) long.

The river was initially called Mohelnice. The name of the river was derived from the Czech word mohyla (i.e. 'mound', but formerly also 'hill'; so the word mohelnice meant "water flowing between hills"). Mohelka is a diminutive form of Mohelnice.

The Mohelka originates in the territory of Jablonec nad Nisou in the Jizera Mountains at an elevation of 608 m (1,995 ft) and flows to Mohelnice nad Jizerou, where it enters the Jizera River at an elevation of 220 m (720 ft). It is 41.6 km (25.8 mi) long. Its drainage basin has an area of 176.5 km (68.1 sq mi). The average discharge at its mouth is 1.82 m/s (64 cu ft/s).

The longest tributaries of the Mohelka are:

Tributary	Length (km)	Side
Ještědka	13.3	right
Malá Mohelka	12.8	right
Oharka	9.0	right

The river flows through the municipal territories of Jablonec nad Nisou, Pulečný, Rychnov u Jablonce nad Nisou, Rádlo, Hodkovice nad Mohelkou, Žďárek, Paceřice, Sychrov, Radimovice, Vlastibořice, Bílá, Český Dub, Všelibice, Kobyly, Chocnějovice and Mohelnice nad Jizerou.

There are 102 bodies of water in the basin area, but none of them is notable and their total area is only 7.3 ha (18 acres).

The Mohelka is suitable for river tourism. About 15 km (9 mi) on the lower course of the river is navigable all year round.

• List of rivers of the Czech Republic

• River flow at Chocnějovice station – Flood Warning and Forecasting Service of the Czech Hydrometeorological Institute