The Dirty Dam and associated Dirty Ditch were installed in the mid-1850's as part of the ground-breaking Loch Katrine water project.
They were designed to remove sand and silt from surface waters entering the Craigmaddie and Mugdock reservoirs.
Georgina Reid, Scottish Water's corporate affairs manager in the west said: "Over the years there has been a significant build-up which is affecting the efficiency of the network and needs addressing.
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"We anticipate removing approximately 7,000 cubic metres of silt – enough to fill three Olympic-sized swimming pools - over the course of the project.
"It is testament to the ingenuity and engineering prowess of the Victorians that the system is still working and still delivering clean, fresh water to over a million people in Glasgow after so many years."
Preparatory works will begin on Monday 27 February ahead of de-silting operations which are expected to be completed by the end of June.
The dredged materials from the dam will be stored in an abandoned quarry close to the reservoirs to minimise any environmental impact.
Footpaths within the work area and around the northwest corner of the Milngavie Reservoir site - from the Dirty Dam and surrounding woodlands up to the Milngavie Water Treatment Works entrance gate - will be closed to the public for health and safety reasons, and members of the public are being asked to follow the signs.
