BELVIDERE, Ill. (AP) – Presence of a rare mollusk has delayed repairs to a bridge in northern Illinois.

The Rockford Register Star reports that the Belvidere Public Works Department’s plans to repair a bridge five miles west of downtown will have to wait until 2017. That’s because the Illinois Department of Natural Resources needs to determine if a colony of black sandshell mussels should be removed from the Kishwaukee River.

The IDNR classifies the mussels as a threatened species. Public Works Director Brent Anderson says the process needs to happen during the summer, which means the city will lose that construction season.

IDNR conservation biologist Lisie Kitchel is a mussel expert. Kitchel says water clarity is affected when mussels die. Kitchel says the black sandshell population in northern Illinois is rebounding, but slowly.