Water beetles collected from Lake Tonga (North-East of Algeria), one of the best preserved and biodiverse coastal habitats in North Africa, have been studied and identifications of species reassessed, since most previous determinations published in Mahmoudi et al. (2023) were found to be incorrect. In this paper a revised species list is provided, with a small batch of previously unidentified material collected from a second biotope, Garaat Djamel, located 60 km west of Lake Tonga. A total of 42 species were identified, belonging to the families Gyrinidae, Haliplidae, Noteridae, Hygrobiidae, Dytiscidae, Dryopidae, Helophoridae, Hydrochidae, Hydrophilidae, and Hydraenidae, hosting approximately 13% of the Algerian aquatic beetle fauna, with the vast majority of this diversity concentrated in Lake Tonga, underscoring its status as a key hotspot of aquatic beetle biodiversity in the region. Five of the identified species are new records for Algeria: Helophorus cf. paraminutus Angus, 1986, Amphiops senegalensis (Laporte, 1840), Enochrus natalensis (Gemminger & Harold, 1868), Crephelochares ?livornicus (Kuwert, 1890) and Ochthebius fallaciosus Ganglbauer, 1901. Hydrochus grandicollis Kiesenwetter, 1870, and Coelostoma hispanicum (Küster, 1848), recently recorded from Algeria, but omitted from major catalogues, are here confirmed for the country. Furthermore, the discovery of a male of the poorly known Haliplus ruficeps Chevrolat, 1806 represents the first documented record of this species in more than a century. Photographs of the habitus and male genitalia of H. ruficeps and of the newly recorded species are provided. At present, Algeria supports 301 species of aquatic Coleoptera across 84 genera and 17 families. A comprehensive and updated checklist is also given, with a discussion on several doubtful or unconfirmed records.
