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).
The hydronym Szywra refers to the small river in the Warta basin flowing in the central part of Greater Poland. Although its name remained unclear for most of the researchers, it was believed to be of Pre-Slavic or Balto-Slavic origin. The paper reveals that these hypotheses were based on the wrong interpretation of the source material, and provides a new etymology for the name Szywra. Based on the critical analysis of all of the reachable records of names referring to the river Szywra, it has been proven that its Polish name is an adaptation of the former German name Schieferbach. Such a process was possible due to the long-term bilingual situation in the region of Greater Poland.