Brent Council is appealing to local people for help in catching thieves who have stolen 95 manhole covers costing almost £31,000.
The thefts in the last two months have been of metal grates used to drain water off roads which are thought to be sold for scrap metal.
It is understood they fetch about £10 at scrap metal yards although the council has to pay £325 for a new one.
Dangerous holes are being left uncovered and the council is working hard to make the areas safe by using cones and covering the hole with plywood until the covers can be replaced.
Although Brent has had the problem in previous years, the high number of thefts is unusual and smaller roads with no CCTV are being targeted.
Brent is not alone with its recent spate of missing manhole covers as other London boroughs have also previously reported being hit.
Councillor Daniel Brown, Brent Council's Lead Member for Highways and Transportation, said; "The council has already contacted scrap metal yards about the issue and we will be taking a hardline with the thieves responsible.
"We are concerned that people may injure themselves because of these holes. The metal grates are also costly to replace and a waste of taxpayer's money."
If people spot the drain holes left uncovered or see people working on the road without any official markings on vehicles or clothes, they can call the council on 020 8937 5050 to report the problem.
Residents can also contact their Metropolitan Police Safer Neighbourhood Team at
www.met.police.uk/brent or via the police switchboard on 020 7372 12 12.