The second stage of work to restore the Captain Cook Memorial Jet is under way, but the National Capital Authority warns it may not fully return to its former glory.
Work to ensure the water jet in Lake Burley Griffin could operate at its full 147-metre height began this month.
However, NCA chief executive Malcolm Snow said on Tuesday rising energy costs could mean the water fountain would only reach full height on "special occasions".
"Once the jet is operational again, it will run from 2pm to 4pm daily, and whilst we appreciate the community would want to see it operating at its full height, we will need to assess the financial implications of operating it at that height," he said.
"An increase in energy costs may see us limit operating at full height just for special events, occasions and ceremonies."
An NCA spokeswoman said if the dual pump fountain operated at full height, it would cost an extra $250,000 annually to run than if it was operating on a single pump to a height of 110 metres.
The total project is expected to cost just under $3 million, which takes in the refurbishment of the first pump.
The water jet, which is in the central basin of Lake Burley Griffin, is undergoing its first major overhaul in more than 20 years.
The fountain has been out of action since June because of complications from a failure of its pumping system.
The jet was opened in 1970 to commemorate the bicentenary of Captain James Cook's discovery of the east coast of Australia.
It once pumped water 147 metres high for two hours daily.
However, the NCA spokeswoman said it had been operating at a height of 110 metres on a single pump for several years.
Mr Snow described the project's construction management and programming of works as challenging as multiple trades worked together in a confined space two storeys underground.
"The extent of works on this significant project is more complex than we initially imagined and this demanded smart thinking in how we sequenced the program of works. As a result, key electrical, mechanical, hydraulic and fire service works are being undertaken concurrently," he said.
Engineers would continue to assess the condition of the jet's pump, its components and related pipework.
Depending on the pump's condition, the NCA said the project should be completed in the second quarter of next year.