Knajka is a stream in the Cieszyn County, Silesian Voivodeship, Poland, in the historical region of Cieszyn Silesia. It is a left-bank tributary of the Vistula, which it enters just south of Strumieà Â. Its length is variously said to be either or . It flows through Ogrodzona, Kostkowice, DÃÂbowiec, Knaj and Bàków. Numerous fish ponds are located alongside of it.
The name of the river is derived from a word knieja denoting a wild, dense forest.