Two young men had to be airlifted from the island at the south end of Clickimin Loch in the early hours of Sunday morning during the Relay for Life event.
The pair had been on the loch in a dinghy which had deflated, and although they made it to the isle safely, they needed help getting off.
The emergency services were called and Lerwick police alerted Shetland Coastguard shortly before 1am to say the aircraft was needed. However, at the same time the Sumburgh-based helicopter Oscar Charlie was attending to a medical evacuation from Unst as a priority.
The casualty from Unst was airlifted to the Clickimin landing site in Lerwick and the helicopter then nipped over to the island, where the two youths were winched on board.
The police said this week they had given the two advice about safety.