The steel covers, which are usually located on the outside edge of sidewalks, cost about $100 to replace. (CBC)

The City of Ottawa is warning road users — particularly cyclists — to watch out for gaping holes along the sides of roads after about 150 catch basin covers disappeared in the past month.

About 75 of the rectangular or square steel sewer grates, which are found at the edge of the road, next to the sidewalk, have been stolen in the past week alone, Marco Lalonde, the city's manager of surface operations, said Thursday.

Each one weighs 27 to 59 kilograms, covers a hole up to three metres deep, and costs about $100 to replace.

The thefts of the covers are under investigation by the Ottawa Police Service and the city's corporate security branch, the city said in a statement Thursday.

So far, the city knows of no one who has been hurt as a result of falling into an open hole.

The covers have mostly been purloined in the middle of the night. Normally, the city loses very few "if any" each month, Lalonde said.

The city is asking residents to call 311 if they discover any open holes. A worker can arrive in 30 minutes to an hour, and will at least ensure the hole is covered and secured if the cover cannot be replaced immediately.

Lalonde said he knows the price of steel has soared in the past year or so, and he suspects thieves who want to sell the scrap metal — not pranksters — are responsible for the rash of missing covers.

"Pranksters will usually just drop them in the bottom of the catch basin," he said, adding that the covers are easily recovered from there.

Coun. Peter Hume, who represents the Alta Vista ward, where a number of grates have gone missing, said Ottawa scrap metal dealers are being told not to accept such materials.

"It's dangerous for cyclists, it's dangerous for pedestrians, it's dangerous for children, and it's not something that the city is going to tolerate."