An 80-year-old man visiting Grand Canyon National Park died after his boat flipped in the Colorado River, park authorities said. 

The incident unfolded Sunday around 3:40 p.m. near Fossil Rapid on the river. 

The Grand Canyon Regional Communications Center was alerted about an emergency via satellite phone that the man had entered the river after his boat flipped and was being treated with CPR. 

“Despite the efforts of the group and park rangers flown in by helicopter, all resuscitation attempts were unsuccessful,” the National Park Service said in news release. 

The victim was not identified. His death is under investigation by the park service and the Coconino County Medical Examiner. 

The man’s death marks at least the fourth fatality at the park this month alone, according to park announcements thus far.

Also Sunday, at 11:30 a.m. local time, the body of Chenoa Nickerson, 33, from Gilbert, Arizona was found by a commercial river trip in the Colorado River. Nickerson had been reported missing following a flash flood that hit Havasu Canyon on Aug. 22, and her body was found nearly 20 miles from that area, park officials said. 

On Aug. 6, the body of 20-year-old Leticia A. Castillo of Albuquerque, New Mexico, was found 150 feet below the rim of Twin Overlooks along Desert View Drive following a multiday search, the park said. She was believed to have entered the Grand Canyon on or around Aug. 3. It’s not clear exactly what caused her death.

A few days earlier on Aug. 1, an unnamed man died following an attempted BASE jump from Yavapai Point on the South Rim of the park. His body was found 500 feet below the rim, along with a deployed parachute, authorities said.