Fish and amphibians in the Santa Cruz River were killed after officials involved in the Ina Road construction project redirecting the effluent flow feeding the river.
The Ina Road project, led by the Arizona Department of Transportation and the Town of Marana, moved water from the river’s west bank to the east bank, which trapped fish in isolated pools as the water level lowered.
A press release put out by the county said the flow diversion was necessary for construction of a bridge and that county biologists estimated the number of fish killed was a small percentage.
“While the death of fish is unfortunate and may be upsetting to visitors to the river and users of The Loop, there is no practical way to remove these non-native fish when channel flows must be changed for work in and along the river,” the press release reads.
After the river’s natural flow was staunched decades ago, due to people pumping it for farming and other uses, 23 miles of the river were restored thanks to the treated wastewater and seasonal storm runoff.
The number of fish and amphibians in the river has multiplied since 2013 due to improvements to the two county wastewater treatment plants, lowering the levels of ammonia and nitrogen in the reclaimed water being added to the river.
As far as where the non-native species came from, researchers speculate people transferred them from nearby lakes and ponds.