The research was conducted in July 2018 on six oxbow lakes of the San River. A total of 21 samples from various macrophyte species were collected. Over 400 species of diatoms were identified in the analyzed materials, 9 of which belonged to the Rhopalodiaceae family. Most of these Epithemia and Rhopalodia species developed as dominants in most of the studied samples. One of reported species – Epithemia selengaensis Vishnyakov, Kulikovskiy & Genkal was first time reported from Poland. The aim of the study was to present the taxonomic diversity of the representatives of the Rhopalodiaceae family growing different macrophyte species in oxbow lakes in the summer aspect.