A 39-year-old Brooklyn man lost his life on Sunday at Napeague Harbor in Amagansett, where he had gone to kite surf. His death was the first of two on the water that day. That evening, James A. Weber, an East Hampton man who was to have celebrated his 45th birthday yesterday, died after collapsing in shallow water on the west side of the Three Mile Harbor inlet near Sammy’s Beach in East Hampton. Nicholas Valtz, a managing director at Goldman Sachs Group in Manhattan, left his house in Bridgehampton early Sunday for Napeague Harbor. When he failed to return, his family, who called 911 at 2:02 p.m., went to look for him. They found his body in the water near the beach at the end of Lazy Point Road, according to police. Mr. Valtz, a married father of two young children, was described by police as a novice kite boarder. The Amagansett Fire Department ambulance was called, but he was pronounced dead at the scene. An autopsy report from the Suffolk County Medical Examiner was pending at press time. Town Police Capt. Chris Anderson said Mr. Valtz “was found floating in the water secured to his kite and associated kite gear in a grassy area of the harbor.” Captain Anderson said it is always a good idea for those on the water to go out with others in case of an emergency. Like other water sports, kite boarding comes with its dangers. The sport employs the use of a bar with lines and a harness to attach the surfer and a board to the kite. Websites about the sport recommend the use of helmets, booties, and even a hook-knife to cut lines if necessary. On Tuesday, Captain Anderson said police were exploring every possibility from some sort of an accident to a medical event to try to learn what happened. However, he said, “There is no indication that he became entangled to the point where he lost mobility.” Captain Anderson said it was unclear how long he had been the water. He had been alone, but had been seen by other kite surfers, Captain Anderson said. However, he said, “We do not have anyone who saw whatever happened to him.” The East Hampton Village Ambulance Association was called to Three Mile Harbor later on Sunday, and rushed Mr. Weber to Southampton Hospital, where he was pronounced dead. Two good Samaritans on the east side of the inlet, whose names police did not release, saw Mr. Weber collapse. The men swam across the inlet from Maidstone Park Beach, which took several minutes, and pulled him out of the water. He was unconscious, and they attempted cardiopulmonary resuscitation until emergency personnel arrived. The 911 call came in at 7:19 p.m. The Suffolk County Medical Examiner is assisting detectives in determining what led to Mr. Weber’s death. A lifelong resident of Northwest Woods, Mr. Weber was a carpenter. No funeral arrangements had been made as of press time, according to his brother, Tim Weber. An obituary will appear in a future edition. Anyone with any information about either of the two incidents has been asked to call town police at 537-7575.