'Covering of ice' on River Foyle
The Loughs Agency has warned people not to venture onto icy rivers or loughs under any circumstances.
Ice has formed on rivers, loughs and canals across Northern Ireland in recent days, and on Thursday morning a thin covering stretched right across the River Foyle.
Andy Sides, development officer with the Loughs Agency, said conditions were "very dangerous".
"This is only a covering of ice. The water is not frozen."
"Our fear would be that people would start to walk on the ice because they think it is frozen.
"If they break through the ice they are likely to drown, or die from exposure.
"Our advice is not to go near the ice at all."