NHS Highland has warned of a "significant pressure" on staffing levels in its mental health service.
The health board has 33 vacancies, 25 of them for registered mental health nurses, at its New Craigs Hospital in Inverness.
The situation has led to a temporary reduction in general adult beds.
NHS Highland said repeated efforts to recruit staff to fill gaps at the hospital and in the wider service had been unsuccessful.
The health board's Michael Perera said nurse staffing levels in the mental health service of the Inner Moray Firth area had been under pressure since November 2016.
But he said gaps in the rota were now happening on a daily basis.
Mr Perera, who is general manager for NHS Highland's mental health services, said: "There is a significant shortage across the UK of mental health nurses.
"Our efforts to recruit, which have included attending four recruitment fairs across the UK, adverts in national journals and recruitment websites have been unsuccessful in attracting enough staff to meet the gaps that we have.
"In addition, nine of our current establishment of trained mental health nurses have indicated their plans to retire this year."
He added: "This has left us with a significant pressure within inpatient services and if we don't act now the safe running of the hospital is at risk.
"General adult beds within the hospital have been temporarily reduced from 48 to 42 while we continue to look at all options available to us in terms of staffing and the current and future demands of the service."