The bubble-nesting Betta smaragdina Ladiges, 1972 can be distinguished from the 4 other species of bubble-nesting Betta Bleeker, 1850 by being reportedly confined to Northeastern Thailand. We found large populations of fish in Western Thailand that closely resemble those from the Northeastern Region. The new populations inhabit a variety of places encompassing lakes, marshes, and streams. Morphological studies of Betta fish from the 2 well-separated regions, together with DNA analyses, show that the western and the northeastern populations are the same species.