The principal, which was $56.7 million when the fund was set up in 1999, stood at $71 million on September 30.
The fund was established using proceeds from the sale of the Waipori electricity generation scheme and has been a valuable contributor to the council's finances.
A report to the council's finance, strategy and development committee this week from fund chairman Ross Liddell said the most significant contribution, $2.1 million, came from positive market movement in equity portfolios.
Movements in exchange rates and interest rates were also positive.
Council finance and corporate support general manager Athol Stephens told the committee meeting the result was "a good, positive outcome" for the fund.
He noted, though, that the policy for the fund was to grow the capital by the rate of inflation, so its real value did not decrease.
Because the recession had affected results, that policy had not been achieved, something he said the fund's managers were concerned about.
"The fund managers are concerned to ensure that they don't breach the policy of the fund over a long period.
"In the normal course of events, we would expect to work through the cycle, but there's no guarantee of that."
As a result, dividend levels had to remain at the past year's level.
