Eleven Indonesian students of a local junior high school were killed in a drowning incident on Friday, as they participated in a river clean-up drive, leaving parents and teachers concerned about the lack of safety protocols that can be used in keeping the children safe.

Around 150 students were participating in a river clean-up drive for the Cileueur River in Indonesia’s West Java province when a group of 21 students slipped off and fell into the water, causing teachers and other onlookers to panic, according to Deutsche Welle.

“The weather was good and there was no flash flood,” Bandung Search and Rescue Office chief Deden Ridwansyah told reporters. “Those children who drowned were holding each others' hands. One of them slipped and the others followed.”

The students’ ages were between 12 and 15 years old, and many were in danger of being swept away by the strong current of the river. Over 10 of the 21 students were saved, according to the New York Post.

The teachers and other nearby residents attempted to save the children who fell into the water. As the incident intensified, a rescue team was sent to save the remaining students or to collect the bodies of those who drowned. Some of the teachers were injured in their efforts to save the students from drowning in the river.

“Search teams found all of the victims downstream,” Herdiat Sunarya, the district chief, said.

Rescue teams were using inflatable orange rafts to find and account for all the victims of the incident. It is believed that many of the students who fell in the water attempted to cross the river, which is a popular spot for rafting and inner-tubing.

The 10 students who were saved were sent to a nearby hospital to recover. None of the children wore any flotation devices to keep them above water as they were rescued.

The incident has raised questions as to the adequacy of safety surrounding the rivers of Indonesia, as many parents worry that future rains may bring in flash floods from the rivers that may affect the families of the region.

The organizers of the river clean-up are yet to release a statement about the incident.

Eleven students drowned in Indonesia on Friday after a river clean-up drive went horribly wrong as students slipped and fell into the water. This is a representational image. Ibrahim Rifath/Unsplash.