Lake Burley Griffin's Captain Cook Memorial Jet won't be operational until at least June, as the National Capital Authority continues a $2.7 million repair job.
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The jet stopped working in February 2015 after a failure in its underground pumping system caused significant flooding in a chamber below the lake, near Regatta Point.
The jet was restarted in May last year but saw more flooding due to the mechanical failure of a cone valve that controls the flow of water to the jet nozzle from the pump chamber.
Authority briefing documents prepared for Senate Estimates hearings and obtained under freedom of information rules show the failure was caused by the jet being "automatically operated while submerged during the flood event".
"The fault was not identifiable until the station returned to operation," the documents say.
The upgrades and refurbishment works were commissioned by the authority and put to tender in August last year. Shaw Building Group was engaged to complete the work.
Temporary construction fencing has been placed around the entry point to the pump chamber on land adjacent to Commonwealth Avenue near the entrance to Regatta Point.
Once repaired, the jet will be ready to resume its operation from 2pm until 4pm daily.
When fully operational, it can pump water 147 metres into the air and can be seen on the skyline from sites around Canberra. At full strength it sends three tonnes of water into the air at about 260 kilometres per hour.
The documents show the works are scheduled for completion by mid-2016, with an approved budget of $2.7 million. The authority has previously indicated some of the cost will be the subject of an insurance claim.
The jet's irrigation system is contained in the same area as the pump's main system, housed in a chamber big enough to fit three people. Last year authority crews used dehumidifiers to remove as much moisture as possible from inside the pump room, before conducting tests and safety checks of electrical switchboards and circuits.
"The jet costs approximately $365,000 per annum ($500/hour of operation) including the programmed maintenance and power," the document shows.
"The jet runs from 2 to 4pm daily. This time was chosen as the most appropriate for visitors to the jet and Regatta Point.
"It also operates out of normal operating hours for significant cultural events and head of government visits, such as Australia Day and the G20."
The jet was opened in 1970 to commemorate the bicentenary of Captain James Cook's discovery of the east coast of Australia. Part of its design is based on a similar memorial in Geneva, known as the Jet D'Eau.
Water is drawn from the lake using a 50 metre-long intake tunnel which links to the base of the pump house. A large power line runs under Regatta Point.
Originally costing $320,000 to build, the jet broke down and underwent a ten-month restoration in 1995, costing about $100,000.
Press reports from 1969 show a barge and a weather station were used to test wind patterns and conditions in the area before the design was completed. A series of special balloons were launched from the lake's central basin to determine how high water could go into the air.
The jet was commissioned after a committee looked for a memorial to Captain Cook in the 1960s. A rival proposal to build a replica of Cook's ship, the Endeavour, was deemed too expensive.
