| Knajka | |
| Source1 Location: | Chełm Hill, Silesian Foothills[1] |
| Mouth Location: | Vistula |
| Mouth Coordinates: | 49.9051°N 18.7584°W |
| Subdivision Type1: | Country |
| Length: | 17km (11miles)[2] or 19km (12miles)[3] |
| Source1 Elevation: | 354m (1,161feet) |
| Basin Size: | 68.6km2 |
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 Strumień. Its length is variously said to be either 17km (11miles)[1] or 19km (12miles).[3] It flows through Ogrodzona, Kostkowice, Dębowiec, Knaj and Bąków. Numerous fish ponds are located alongside of it.
The name of the river is derived from a word knieja denoting a wild, dense forest.[4]