Portland police are investigating the theft of a large number of cast iron manhole covers and sewer grates from city streets over Sunday night.

Residents began reporting the uncovered holes in the Washington Street Extension area to the city’s public services department this morning.

The coverings weigh up to 300 pounds and cost about $130, police said.

Police were notified by Schnitzer Steel on Somerset Drive that 13 of the covers were discovered in their scrap pile. The company said it does not accept the covers as scrap because most of the time they are stolen and because stealing them endangers the public, police said.

Police suspect the heavy covers were buried in a load of legitimate scrap.

Fourteen of the covers had been reported missing to the city and workers had already started installing replacement covers it keeps on hand, a city spokeswoman said.

A person who steals the covers is committing theft and possible aggravated criminal mischief, police said.