Two French sisters, 16 and 19, who didn’t know how to swim drowned in a hotel pool on the island of Rhodes during a time when their was no lifeguard on duty, leading to a prosecutor ordering the arrest of the managers to face questioning, the state-run Ahens-Macedonian News Agency reported.

The parents of the girls, who weren’t identified, said the family was on holiday but it wasn’t explained what they were doing in the pool if they couldn’t swim even only a few feet to shallower water or to the pool’s edge.

The incident happened after 6 p.m. July 31 said Kathimerini, shortly after the lifeguard went off duty during daylight hours with no details why the hotel didn’t keep a guard at the pool longer during the summer season or if there were any other people swimming there.

It appears from CCTV footage that not finding a lounger beside the shallow paddling pool, the two sisters decided to try a deeper pool at the resort, which has three swimming pools, the report added.

Guests later saw the 16-year-old floating unconscious on the surface of the water and paramedics were called but it was too late to save her. The 19-year-old was found at the bottom of the pool a couple of hours after her parents realized she was missing as her body wasn’t visible.

Investigators believe that the 19-year-old drowned trying to save her younger sister. The family has two other children. The hotel wasn’t named.

In Athens, meanwhile, Tourism Minister Haris Theoharis contacted French Ambassador Christophe Chantely to express his and Prime Minister Kyriakos Mitsotakis’ condolences over the teenagers’ death and say an investigation was underway.

In June, a 5-year-old British boy drowned in a hotel pool on the island of Kos when he wandered out of his family’s room while his parents were sleeping in another tragedy.