Semiaquatic bugs (Hemiptera: Gerromorpha) comprise about 1,800 extant species classified in eight families. So far, 38 fossil species belonging to six families have been described or recorded, most of Cenozoic age. Knowledge about the evolutionary history of the major groups of Gerromorpha is seriously hampered by the scarcity of well-preserved Mesozoic fossils, especially from the Cretaceous. The present paper reports on a well-preserved semiaquatic bug from amber collected in the northern part of Myanmar (Burma). The source of this fossiliferous amber was previously considered to be Eocene in age, but recent evidence indicates that it originated in the Middle Cretaceous (Turonian-Cenomanian), or 100-90 Ma. The fossil species is described as Carinametra burmensis gen. et sp. n. The presence of three pairs of cephalic trichobothria, a prolonged head, long slender antennae and legs, reduced wing venation, etc., places the fossil in the gerromorphan family Hydrometridae or water measurers. Other characters suggest a close relationship with the two extant genera of the most basal of the hydrometrid subfamilies, Heterocleptinae. We present and discuss the available evidence used in the dating of Burmese amber. Finally, we discuss the phylogenetic, paleobiological, and biogeographic significance of the new fossil.