Contriving a landscape fit for the national capital hung heavily on the new Scrivener Dam, which filled with drought-breaking rain in October, 1964 to a new, picturesque brim.

In March this year, 55 steps down into a submerged gallery beneath Scivener's surface, and decades on from the dam building era, Peter Beutel grasped his own dam building moment.

"One of the happiest moments of my working career here was to turn the sluice gates off so we could lift the lake level back up again earlier this year, so everyone could have the full use of the lake as it was intended," Mr Beutel, the National Capital Authority's asset manager, said.

The lake's level had been lowered to ease pressure while anchor bolts on the dam wall were replaced. This left rowers with a rocky path into the water to launch their craft and a traditionally beautiful lake looking leaner and a little meaner.

With the level restored, on a breathless spring morning the water sits still as a millpond.

Scrivener Dam's gallery grinds noisily away below, maintaining the ornamental and recreational level from Yarralumla all the way to Acton, Civic, Parkes and Kingston.

The sound of cars crossing the bridge above fill the gallery with a sharp echo, an ear-splitting phone rings for maintenance workers above the noise of a river flowing through one of three sluice valves, making its way down stream. At night lions roar eerily from the neighbouring National Zoo to fill the void.

Coffins gouged from Queanbeyan cemetery during a flood decades ago which floated down the river, riderless bikes, dead dogs and kangaroos and urban toxins have for half a century settled out of sight on the lake's bed behind the five fish-belly gates that hold the bulk of the water back.

"This design is fantastic if you want pin-point, millimetre accuracy on your lake, " Mr Beutel said. "Most dams don't [have that accuracy], most are built entirely for water supplies, for irrigation or for flood control."

Surveyor Charles Scrivener not only recommended the site, but the water level of 556 metres above sea level, which is faithfully maintained from within the spotless, well-lit gallery.

Telemetery readings from various points of the lake and catchments of Molonglo and Queanbeyan Rivers, Sullivans and Jerrabomberra creeks feed computers which tell dam operators what water is on its way.

The controls system will have a $1 million upgrade next year, and yet some things never change beneath Lady Denman Drive.

Under each of the four hydraulic rams thatoperate the fish-belly gates sits a red plastic bucket. If seals on the rams perish over time, oil will be caught in the bucket and alert maintenance crews. "Low tech, but very effective," Mr Beutel said.

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