It is understood the man, who was in his 20s, died on Tuesday after a tree fell on him as he worked at Slieve Gullion Park in Co Armagh.
Another man in his 40s was injured. Both men were doing work for NI Water at the time of the incident.
In a statement, NI Water said: "NI Water is aware of an incident involving employees of one of our contractors. Emergency services attended to two individuals. Sadly one of these people died at the scene.
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"NI Water is currently working closely with the Emergency Services, the Health and Safety Executive and the PSNI and will do everything possible to assist.
"Our thoughts are with the families of those involved at this time."
SDLP MLA for Newry and Armagh, Justin McNulty, also extended his condolences to the family of the victim.
"It is extremely upsetting to hear that a man has lost his life as a result of today's (19 September) weather conditions," he said.
"It is sometimes too easy to forget the danger workers during adverse conditions face to keep the public safe. I want to send my condolences to his friends and entire family circle at this terrible time.
"I also want to take this opportunity to ask constituents to take care and remember the danger that can come with such extreme weather."
(LM/MH)
