This article deals with the name of the town Węgrów on the river Liwiec, whose name is based on the obscure hydronym Węgra Potok. This name is juxtaposed with another place name, Węgra, which is found near Przasnysz and is named after the river Węgra (today known as Węgierka), as well as other names beginning with wągr-||węgr-. The author challenges Witczak’s (2015) hypothesis that the name of Węgra comes from the Sudovian (Jatvingian, Yotvingian) language. The article raises historical, archaeological and geographical arguments that oppose the possibility of a Yotvingian influence in these regions. Consequently, the author contends that the place names have a Slavonic root, linked to the noun węgorz (a type of fish), or the meandering nature of both rivers. There is also a discussion of the name patok||potok (stream/brook).