During a survey of the diatoms from French Pyrenean lakes, a new species of Cymbopleura, Cymbopleura pyrenaica sp. nov. was found. The detailed morphology of this taxon was examined using light and scanning electron microscopy. The new species most closely resembles Cymbella laevis Naegeli, but the absence of apical pore fields places Cymbopleura pyrenaica in the genus Cymbopleura. The most conspicuous ultrastructural feature is the morphological variability of the areolae. Cymbopleura pyrenaica sp. nov. was recorded in several lakes despite its low occurrence and tolerates a wide range of conductivity. A short review of the scarce Cymbopleura species in the investigated lakes was presented.