Abstract Lake Pamvotis (= Lake Ioannina) is an ancient lake in NW Greece famous for its long geological record, which has furnished some of the most detailed Quaternary palaeoclimate records from Europe. Unlike some other Balkan lakes, which exhibit spectacular faunal radiations, Lake Pamvotis (and its surrounding habitats) supports just two (but maybe up to five) endemic gastropods but is the type locality for two other valid species of aquatic molluscs and for two taxa now regarded as junior synonyms. It was also an important locality where Schläfli collected specimens later described by Mousson in 1859. These shells, now in Zürich Museum, have been revised as part of a new study of the aquatic fauna of the lake. Four species represented in this collection are not otherwise known from Greece, raising the suspicion that shells from different localities have become mixed. The status of a further two species, known elsewhere in Greece, remains unclear since they have not been re-discovered at Ioannina. A systematic review is given of the 29 species of gastropod and 8 species of bivalve now known from Lake Pamvotis and its surrounding marshlands and springs. Trichonia trichonica is reported from only its second known site and Pisidium obtusale and Gyraulus cf piscinarum are recorded from Greece for the first time. Illustrations of critical taxa are presented. Planorbis janinensis is transferred to the genus Gyraulus. Eight species of mollusc have been recovered from Holocene sediments beneath the lake; the records for four of these can be traced back to at least 200,000 years. Dreissena stankovici seems to have been present at Ioannina throughout the Quaternary.