The Oleška is a river in the Czech Republic, a left tributary of the Jizera River. It flows through the Liberec and Hradec Králové regions. It is long.
Etymology.
The name is derived from the Czech word "olše" (i.e. 'alder'), meaning "water flowing between alders".
Characteristic.
The Oleška originates in the territory of Studenec in the Giant Mountains Foothills at an elevation of and flows to Semily, where it enters the Jizera River at an elevation of . It is long. Its drainage basin has an area of .
The longest tributaries of the Oleška are:
Course.
The river flows through the municipal territories of Studenec, Levínská Olešnice, Stará Paka, Bělá, Libštát, Košťálov, Slaná and Semily.
Fauna.
Fish species that live in the river include brown trout, rainbow trout, brook trout and grayling.