A mother drowned and her husband and children were rescued when the family got into difficulty while swimming on Friday.
The Indian woman, 32, was pulled from the sea off a beach in Umm Al Quwain.
Her husband, 49, and twin children, 4, were saved.
Members of the public ran to help the father as he tried to swim out to his wife, UAQ Police said. Police and marine rescue arrived soon after.
All four were taken to a nearby public hospital where the mother was pronounced dead.
The children and their father are in a stable condition, said police Brig Khalifa Al Shamsi.
He urged beachgoers to take care in the water, wear life jackets if they are weak swimmers and keep a close eye on their children.
The women's death was the third such tragedy this week.
On Tuesday, a five-year-old boy who spent 50 days in intensive care died as a result of a swimming accident.
Zaid Al Shehhi was pulled unconscious from the water at Al Maahad beach on April 4 after getting into difficulty while swimming.
He suffered brain and organ damage relating to oxygen loss.
In a further tragedy, a friend of Zaid's family drowned in an accident on Thursday.
Abdul Aziz Al Shehhi, 14, was pulled from the water dead after getting into trouble while swimming off Al Rams beach in Ras Al Khaimah.
Dr Ammar Al Hakim, head of the paediatric unit at Ajman's Sheikh Khalifa Medical City, one of the largest hospitals in the Northern Emirates, urged parents and lifeguards to be alert.
“Pulling a child out of the water doesn’t mean they are safely rescued, because a body deprived of oxygen can lead to severe repercussions," he said.
It can prove fatal hours after the accident, if medical treatment is not sought.
"I'm saddened by this and its an eye opener for all parents to be more cautious," he said. “Never allow children to swim without armbands."