ANN ARBOR, Mich. (AP) — Officials say an estimated 300,000 gallons (1.1 million liters) of sewage spilled at the University of Michigan Arboretum due to a blocked sewer line.

The city of Ann Arbor says it was notified Sunday of water leaking from a manhole at the arboretum and crews discovered it was a sewer overflow. Crews cleared the line and started working on cleanup.

The city says sewage flowed into Dow Prairie and some ended up in the Huron River. Affected areas of the prairie were closed for cleanup and people were advised to stay off the river.

The line was blocked in part by 3,000 feet (914 meters) of rope that the city says belonged to a contractor who recently lost it while inspecting sewers. An uninflated sewer plug also was found.