People swimming under ice in Antrim are putting their lives at risk, it has been warned.
Lough Neagh Rescue has also pleaded with people not to walk on frozen ice ponds at Antrim's Castle Gardens and raised the alarm over swimmers jumping into the lough through frozen ice.
In a statement on social media, Lough Neagh Rescue Service said: "It might look like fun and you might think it's safe to walk or swim under the ice but the consequences of your actions could be severe and life threatening. Unfortunately we have witnessed the consequences of this before."
The rescue service said it had received "lots of calls and messages" in relation to incidents at Long Ponds, Clotworthy House and at the lough in Antrim.
Lough Neagh Rescue added: "We would encourage our followers to keep safe and follow current safety guidance. Please keep safe and in case of an emergency dial 999 and ask for the Coastguard."
A warning has also been issued by the PSNI.
Police in Antrim and Newtownabbey said: "Neighbourhood officers in Antrim have had to warn young persons from standing on the ice in the pond in Antrim Castle Gardens.
"This is a very dangerous thing to do as the thickness of the ice cannot be determined.
"With the health service stretched at the moment, please consider your own safety. Do not stand or skate on this ice."
Antrim and Newtownabbey Borough Council said: "Please be aware of the danger of frozen ponds and don't risk walking on them."