Muck, Flotta and Foula struggle to recruit firefighters
The Isle of Muck could lose its community firefighting unit if difficulties recruiting enough people to deal with a blaze continue.
Flotta in Orkney and Foula in Shetland, have also had problems with recruitment, according to Highlands and Islands Fire and Rescue Service.
The isles' low populations and few incidents make maintaining crews hard.
Fire chiefs have recommended that recruitment campaigns continue on Muck to add to its five personnel.
However, closure is a possibility if problems persist.
The details are contained in a report to Highlands and Islands Fire Board setting out how cover should be provided in Highlands, Western Isles and Northern Isles.
Eigg, which like Muck is one of the Small Isles, has managed to recruit sufficient numbers.
It has nine personnel but there have been so few incidents that HIFRS has not been able to assess the unit's effectiveness, according to the report.
Recruitment problems have also been noted on Flotta and Foula, but there has been no suggestion of closing the stations.
They could instead be re-designated as community response units (CRUs).
Fire board members will be asked to consider the reports' recommendations when they meet on Friday.