The Mail & Guardian reported in early October that the sinking fund, primarily used to offset future debts, was being managed by Regiments Capital – a company with links to the ANC via Johannesburg mayor Parks Tau.
At a press briefing on Wednesday, the DA said it "received proof" from an anonymous tip-off that R1-billion had been siphoned off from the fund since 2006 – the year in which Regiments took over the fund.
"It is imperative for the mayor to account to these allegations and in the long term decide if he is fit to lead the city with this hanging over his head," DA Johannesburg caucus leader Mmusi Maimane told reporters.
A company called Coral Lagoon Consortium was in part set up by Regiments after it received a tender to manage the city's sinking fund.
Individuals connected to the ruling party benefited handsomely from Coral Lagoon, a consortium that acquired shares in Capitec Bank in 2006 with the help of R285-million loan from the Industrial Development Corporation.
One beneificiary is the mayor's wife, Pilisiwe Twala-Tau.
Besides Regiments allegedly charging exorbitant fees for managing the fund, the DA further alleged it has proof that city officials were complicit in ensuring fraudulent transactions were made from the fund.
"This is the public's money and officials must be held to account of how it is managed and administered," added Maimane.
Accordingly, the DA has challenged the mayor to address the allegations to prevent corruption "taking root" in Johannesburg.
In the aftermath of the initial M&G report, public protector Thuli Madonsela confirmed she would be investigating the corruption allegations.
Both Tau and the city have maintained innocence throughout the allegations.
In light of the fresh allegations though, Tau's spokesperson Fred Mukoko and city officials refused to immediately comment.
"We must be careful as to how these matters are dealt with, we will comment in due course," Mukoko told the M&G.