The Middle Rio Grande is the largest region of the Upper Rio Grande basin. It includes one of the largest municipalities in the basin, Albuquerque, and one of the largest reservoirs on the Rio Grande at Elephant Butte, which lies at the southern edge of the region. The Middle Rio Grande is home to an iconic species of the Rio Grande: the silvery minnow. Once abundant throughout the basin, decades of overfishing has left this native fish critically endangered and limited in range. Today, efforts to conserve the silvery minnow include monitoring for the fish river mile by river mile in the Middle Rio Grande.