The Třemošná is a river in the Czech Republic, a left tributary of the Berounka River. It flows through the Plzeň Region. It is 43.7 km (27.2 mi) long.

The name Třemošná evolved from the word střemcha, i.e. 'bird cherry'.

The Třemošná originates in the territory of Krsy in the Rakovník Uplands at an elevation of 600 m (2,000 ft) and flows to Kaceřov, where it enters the Berounka River at an elevation of 278 m (912 ft). It is 43.7 km (27.2 mi) long. Its drainage basin has an area of 249.2 km (96.2 sq mi). The average discharge at its mouth is 0.62 m/s (22 cu ft/s).

The longest tributaries of the Třemošná are:

Tributary	Length (km)	Side
Bělá	21.1	left
Zlatý potok	8.3	left
Nekmířský potok	8.0	left

The river flows through the municipal territories of Krsy, Úněšov, Všeruby, Nevřeň, Příšov, Ledce, Třemošná, Česká Bříza, Hromnice, Jarov and Kaceřov.

There are 180 bodies of water in the basin area. The largest of them is the fishpond Hamr with an area of 13.4 ha (33 acres), supplied by the Bělá. A system of several small fishponds is built on the upper course of the Třemošná.

• List of rivers of the Czech Republic

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