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.
Four churches share £200,000 to tackle urgent repairs
By Claudia Savage (Press Association)
Irish leaders condemn fuel protests as wrong and ‘not in the national interest’
By Bairbre Holmes (Press Association)
Police probe suspected arson attack at Coleraine apartment block
By Claudia Savage (Press Association)
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)
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