Police in Zuid-Holland are investigating the mysterious deaths of three men who were found dead in a luxury motor boat moored on a canal just outside the village of Wateringen on Sunday afternoon.

The three men were two bothers aged 26 and 30 from Leidschendam-Voorburg and a 20-year-old from Zoetermeer. Police say the deaths are not suspicious but that it is unclear what actually happened.

One theory which has been put forward is that they died of carbon-monoxide poisoning. ‘That is one of the scenarios we are looking at,’ a police spokesman said on Sunday evening.