The Liwiec (or Liw) is a river, in the plains Podlaskie and Masovian voivodeships. It is 126 kilometres long and drains 2779 square kilometres. Its source is located to the north-west of Międzyrzec Podlaski near Siedlce and crosses Wyszków, Liw, Węgrów and Stara Wieś. It finds its estuary into Bug near the towns of Wyszków and Kamieńczyk.

Some parts of the river's flow are extremely winding, e.g. one among the meadows in the neibourhood of so called Sowia Gora (Owls' Mount) between Pierzchaly and Jarnice villages, creating many photographic opportunities.