FLINT, Mich. -- Flint police are investigating the thefts of hundreds of manhole covers and sewer grates.

Not only will the cost to replace the heavy metal fall to the taxpayers, but police said the gaping holes left behind are a serious hazard for motorists.

Authorities said almost 400 manhole covers and grates have been taken in the past year.

The cost to replace them runs between $125 and $170. Police believe scrappers are behind the thefts, which can net them about $20 at metal recycling plants.

Most manhole covers weigh about 100 pounds, but some in heavily traveled areas can weigh nearly 300 pounds.

There is less metal in a steel grate, and they weigh about 70 pounds.