The number of thefts in the Tilehurst and Soutcote areas of Reading has been mounting, the borough council said.
It is believed the iron grills, which cost the council Â£500 each to replace, are being sold for scrap for about Â£2 a time.
"One can only guess what level of moron is stealing these covers," said deputy council leader Tony Page.
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Public safety is at risk after 40 drain covers were stolen within two weeks, a council has said.