Health officials say septic systems are the likely source of wastewater contamination in several private wells near the southwest Idaho city of Nampa.
KIVI-TV reported Tuesday that Southwest District Health and the Department of Environmental Quality completed a review of nine private wells.
Southwest District Health spokeswoman Laurie Boston says none of the wells tested positive for E. coli bacteria but evidence indicates wastewater is starting to affect all the wells in the area.
Officials say there have been no reports of illnesses connected to the contamination.
Health officials are encouraging all well owners to continue testing the water regularly for bacteria.
The first signs of water contamination in wells near Nampa were reported last summer.