An electron microscopy study of phytoplankton from watercourses and water bodies on the Taz Peninsula (mainly the basins of Poilovayakha, Nyudya-Adlyurepoko, and Mongoyuribei rivers) makes it possible to significantly broaden the taxonomic spectrum of Bacillariophyta at the genus and species level—from 181 taxa from 28 genera to 338 species and intraspecific forms from 62 genera. A total of 25 species and varieties new for the flora of Russia are detected; 36 forms from 17 genera are identified only to the genus. The maximum taxonomic variability is recorded in the upper reaches of the Sobetyakha River (106) and in a nameless lake in the lower reaches of this river (91). The following species are the most widespread in the water objects under study: Tabellaria flocculosa, Neidium ampliatum, Achnanthidium helveticum, Nitzsсhia alpina, and Pinnularia sinistra.