COUNCIL BLUFFS, Iowa (AP) — Council Bluffs officials are trying to determine how far invasive zebra mussels have spread from one of the basins where the city draws drinking water from. The Daily Nonpareil reports the mussels were found during maintenance this fall, but it’s not clear if they have begun to colonize and clog the pipes leading into the city’s water treatment plant.

Water Works CEO and General Manager Doug Drummey says the zebra mussels don’t threaten water quality, but they can require costly repairs to clear pipes.The invasive mussels reproduce quickly and then attach themselves to hard surfaces. Drummey says most of the mussels found in September died because the water level was lowered for maintenance. But the pipes leading into the pond will be inspected this month.