Officers from Thames Valley Police have been drafted in to plug a shortfall in security staff at Dorney Lake (officially named Eton Dorney).
A military contingency have taken over part of the security at the site due to complications with staffing schedules and guards skipping shifts.
Assistant Chief Constable for Thames Valley Police John Campbell said a 'small number' of officers have been supporting the security operation.
"Thames Valley Police is experienced in planning for large-scale events and have built contingency and resilience into our plans so frontline policing response and visibility is not in anyway compromised," he added.
Royal Borough of Windsor and Maidenhead councillor Jesse Grey, who represents the council on the Thames Valley Police Authority, said more pressure is being put on the force in the face of funding cuts but filling the shortfall is necessary.
He added: "Officers are being expected to do a little bit extra but I'm sure they'll cope."
The security company has been under-fire since it emerged on Wednesday last week that it could not deliver enough guards to fulfil its £284m contract obligations.
But the exact scale of the problem at the lake is not known as G4S has refused to release the number of absent security personnel. But the venue security control centre is still manned by staff from the company.
Problems with the CCTV network which is still not fully operational have also come to light.
Keith Harris, chairman of Dorney Parish Council said hosting the Olympics at Dorney has brought 'risks' for nearby villagers and the latest security blunder was 'even more concerning'.
He added: "I think it is absolutely shocking. The organisers have had seven years to prepare for the event and it is concerning they are still having problems of this scale.
"They need to get their act together."
Up to 25,000 people are expected to descend on the lake between Saturday and Saturday, August 4, to watch eight days of rowing and canoeing races.
Huge numbers will use transport links set up in Maidenhead, Slough and Windsor.
The games will be the biggest event ever hosted at the venue.
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