Foyle Search and Rescue said one of them could not be recovered, resulting in the local charity having to replace it.
They said lifebelts have been used on 35 occasions to save the lives of members of the public.
In a social media post, they asked anyone who sees people damaging the items to contact the PSNI.
Woman rescued from house in Saintfield following petrol bomb attack
By Rebecca Black (Press Association)
More than 100 firefighters tackle Omagh industrial fire as casualty airlifted
By Claudia Savage (Press Association)
MLAs hit out at ‘Executive chaos’ after U-turn on special school summer schemes
By Grainne Ni Aodha (Press Association)
Delivery driver forced at gunpoint to take object to police station
By Jonathan McCambridge (Press Association)
Elderly woman dies after road collision in Armagh
By Rebecca Black (Press Association)
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