The incident was reported at a private pool at the River Terrace Apartments around 1:30 p.m. on Palisade Avenue.
A 59-year-old woman who was swimming at the time was struck by the tree and pronounced dead at the scene.
Another woman, 72, was taken to the hospital in critical but stable condition.
The NYC Parks department said the tree is not under its jurisdiction.
It is not yet clear what caused the tree to fall.
The incident comes just one day after a man was critically injured by a tree while he was sitting on a bench in Brooklyn.
ALSO READ | 4-year-old riding allegedly stolen scooter with dad killed in NYC crash
4-year-old boy killed in crash involving motorized scooter
----------
* More Bronx news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube