Usually in operation for two hours each day, the jet pumps water 147 metres into the air and can be seen from around Canberra.

However, "a sudden and unexpected failure" of the pump was discovered on February 20, causing its daily operation to be suspended, a spokeswoman for the National Capital Authority said.

An underground pump house was flooded after a key fitting on the irrigation line failed. The irrigation system is contained in the same area as the pump's main system, housed in a chamber below the water and big enough to fit more than three people.

It is not known how long the jet will be out of action as officials are currently investigating the problem and considering how to fix it.

Humidifiers are in place inside the pump room this week, working to remove as much moisture as possible. Electrical switchboards and circuitry will be checked for safety and certified for operation after moisture is removed.

"We appreciate the significance of the Captain Cook memorial jet and are using all available resources and expertise to make the jet operational," the spokeswoman said.

"We will endeavour to advise by the end of the week when the jet will be operational."

When in operation, three tonnes of water are pumped into the air at the site at 260 kilometres per hour, operating from 2pm until 4pm daily.

Located in the central basin of Lake Burley Griffin in front of Regatta Point, the jet was built to commemorate the bicentenary of Captain James Cook's discovery of the east coast of Australia and was opened by the Queen in 1970.

Water pumped through the jet 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.

Part of the jet's design is based on a similar memorial in Geneva, known as the Jet D'Eau. A government guide credits "high-level diplomatic negotiations" for the ability of Australian officials to secure the technical and design specifications of the Swiss fountain.

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 detail how 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 built after a committee considered an appropriate memorial for Captain Cook in the 1960s. A rival proposal to build a full-sized replica of Cook's ship, the Endeavour, was deemed too expensive.

Plans considered by the federal government included building a special memorial pool on top of Capital Hill for the ship, where Parliament House now stands.

An alternative would have seen the replica moored in Lake Burley Griffin.

The jet was chosen instead after it was considered "to be more in keeping with the architectural and civic design concept" of the national capital.