The dam, located in the valley of Maich Water, on the border of Renfrewshire and North Ayrshire, was badly damaged by overtopping during a flood on Friday.
A large part of the downstream face was eroded, leaving a vertical face at the crest of the dam. This edge advanced roughly 150mm upstream over the weekend, leaving around 1m of crest between the vertical face and the water-line.
Consultant Faber Maunsell was called by Strathclyde Police to advise on safety measures for the public.
According to the police, contractors and the Strathclyde Fire Brigade worked through the night to reduce levels. Pumps lowered the water level by about 6m, to reduce the threat of flooding.
The dam has a substantial bypass channel diverting Maich Water around the reservoir, but this had fallen into disrepair. Outlet valves also failed to operate. A temporary reinstatement to the bypass channel was made on Monday, and the water is now diverted around the reservoir.
"The dam is a small earthfall embankment," said Faber Maunsell associate director, Robert Mann. "Its capacity is of the order of 20,000m3, so it does not come under the Reservoirs Act."