Recent surveys have found an endangered native fish in a northwest Tucson in a stretch of the Santa Cruz River that is an historical location for the fish.
Researchers and government wildlife officials say the November discovery of Gila topminnow in a second stretch of the river demonstrates that upgrades to wastewater treatment plants help restore fish habitat by improving water quality.
The diversity of fish species in the stretches of the river downstream of Tucson and Nogales has increased in the past decade following many years during which both sections of the river were so polluted that surveys found few fish of any kind.
With upgrades to treatment facilities, fish can thrive in healthier living conditions that include reduced toxin levels and increased levels of dissolved oxygen.
