MILAN, Aug 30 (Reuters) - Italian prosecutors are investigating a 928 million euro ($1 billion) contract to build a dam off the harbour of the northwestern city of Genoa awarded to a consortium led by Webuild, a person with direct knowledge of the investigation said on Wednesday.

Genoa prosecutors are investigating allegations of bid-rigging, endangering the safety of people and hindering the safety of shipping, the person said.

Webuild, Italy's largest construction company, had no immediate comment on the matter.

The person said there are no individual suspects listed at the moment, adding that the investigation was triggered by a complaint filed at the beginning of August by a retired specialist accounting magistrate.

The complaint called on the judiciary to investigate whether the tender for the contract, commissioned by the Western Ligurian Sea Port Authority and financed with EU recovery plan funds, was tailored to suit the winning consortium.

In May, an administrative court had upheld an appeal from a rival consortium, Consorzio Stabile Eteria, composed of the Gavio, Caltagirone and Icop groups, against the awarding of the works.

The case is now pending before a higher administrative court. Work on the dam is ongoing but the rival consortium could get compensation if it wins its case.

Last month, the National Anti-Corruption Authority (ANAC) in a document indicated eight critical issues in the procedure for the award of the contract. (Reporting by Emilio Parodi Editing by Keith Weir and Nick Macfie)