The plan would see the marina's capacity doubled

A report by independent consultants three years ago listed potential economic gains, including jobs.

But the draft study for Gwynedd Council said fewer jobs would be created and that non-Welsh speakers moving in could have an impact on the language.

The council said the report was the first draft of many into the project.

The authority commissioned the report because of concerns about the potential knock-on effect of the marina plans on the Welsh language.

Some members of the council feared further development could lead to an influx of non-Welsh speakers, and the dilution of the language.

However, the new research, obtained by BBC Wales, has thrown up further doubts.

It questions a previous report which suggested that the marina had created and sustained 257 jobs.

According to the draft language impact study obtained by Radio Cymru's Post Cyntaf programme, the marina currently employs 96 people.

Creating a further 300 moorings - bringing the total to over 700 - would only create a further 17 jobs, the document says.

'Drop in Welsh speakers'

Those supporting the marina expansion have stressed it would be good for the economic development of the area.

The draft study goes on to consider what effect any expansion would have on inward migration, and concludes that, in all, around 217 people would move into the area.

If those people were spread evenly over the whole of the Llyn area, it would lead to 3.3% drop in the number of Welsh speakers as a percentage of the population.

The report suggests that this might not appear significant but, if the incomers are concentrated into one or two villages, then the impact would be more severe and could affect the dynamic balance of the language groups.

A final report is expected within the next few weeks, and the council board is expected to decide whether to expand the marina in early June.

The authority issued a statement saying that the leaked report was only the first draft of one of many reports regarding the marina development.