The Jizera (Polish: Izera, German: Iser) is a river in the Czech Republic and for a brief stretch in Poland.

Smrk in the territory of Lázně Libverda on the Czech side of the border at the elevation of 984 m (3,228 ft) and for centuries it was considered the only source of the Jizera.

Stóg Izerski in the territory of Gmina Mirsk on the Polish side at the elevation of 1,035 m (3,396 ft)), as the source of a headwater that is longer and more substantial than the Czech one, but historically it was a separate stream with a different name.

[2][3] The Jizera flows to Lázně Toušeň, where it enters the Elbe River at the elevation of 169 m (554 ft).

Among the most endangered species are Cochlodina dubiosa corcontica, Daudebardia brevipes, Planorbis carinatus, Clausilia cruciata, Euconulus praticola, Pseudotrichia rubiginosa, Ruthenica filograna, Semilimax kotulae, Vertigo alpestris, Vertigo antivertigo and Vitrea subrimata.

Due to its mountainous character, the upper course is popular among experienced paddlers, but within the entire river there are sections of all difficulties.