The species of the genus Hydraena Kugelann, 1794 of the Baroc River basin in the Philippine Island of Mindoro are studied taxonomically. Five species of Hydraena (Hydraenopsis) are recorded of which three new species, namely H. hinundungan sp. n., H. quirao sp. n., and H. sanvicentensis sp. n., are described. Their genital characters are illustrated by line drawings. Photographs of their habitus and type localities, and a map of the collection sites are provided. Their habitat requirements are briefly discussed and their potential usefulness as bioindicators is deduced. The paper is based on a student thesis and intended as a first step towards the review of the entire hydraenid beetle fauna of Mindoro.