Osława is a river in south-eastern Poland that gets into the San River in the Valley nearby Zagórze. Its length is 55 km and the river basin area is 503 km2. Osława sources flow out from under the southwest Matragona slopes, which is situated in the border strip. Along its almost entire length, The Osława Valley forms the border between Beskid Niski, which is situated within the Western Carpathians and the Western Bieszczady Mountains in the Eastern Carpathians.
One of the prettier sections of the river is the Osława River Gorge under Mokre, which was taken under protection in 2000 in the form of a reserve and the water gap in Duszatyn - also under protection as the "Osława River Water Gap under Duszatyn" reserve. In the river live fish such as chubs, trout, grayling, perch, barbel, and gudgeon. Particularly spectacular is spawning of pig fish – carp-type fish, which begins in early spring. A few thousand of fish swim up the river even from the Vistula River to spawn in Osława. Along the way, the impact of the fins aerates the water so intensively that it looks like it is boiling.