Three people were killed in a deadly accident while tubing on the Dan River in North Carolina, after riding over the edge of a dam. Two tubers are still missing, according to authorities, and a search and rescue operation is underway.

The tubers were members of a nine-person group that went tubing on the Dan River on Wednesday evening. Though they had tied their tubes together, at around 7 or 7:30 p.m., the connection was severed, and several of the tubers drifted apart, some of whom went over the dam.

The dam, which is located near a local power plant, has a steep drop over its edge. The fall likely killed the three individuals whose bodies were found Thursday. Police are hopeful that the two who remain missing are still alive, though it’s too early to tell.

Four of the nine tubers were rescued while “hanging on to various items” on the river at around 3:30 p.m. Thursday. A spokesperson for the Rockingham County Sheriff’s Office, Lt. Kevin Suthard, explained that the four who were rescued were sent to a hospital for treatment and are expected to make a full recovery.

A tweet by the Rockingham County Sheriff’s Office announced that three of the five missing members of the tubing group were found dead, and their bodies have been located and recovered. There is an ongoing operation to recover the two who are missing.

Authorities are searching from the Duke Energy plant near the Dan River to the Virginia State line, according to the sheriff’s office. The operation has included both air and water searches, and also late-night imaging in which officials can heat photographs and detect bodies through difficult terrain.

On Thursday, Rockingham County Emergency Services Director Rodney Cates said that “we have done both air and water search at this time,” just before the three victims had been found. Aircraft have covered an extensive area in its search, including 6 miles into Virginia, as well as an adjacent river in North Carolina. There was another aircraft search planned for late-night Thursday, though it’s unclear if the infrared camera was able to locate the two victims.

“They’ll be able to look at night, pick up heat images at night, in case they were able to get out of the river,” Cates said on Thursday. Authorities have not confirmed any additional findings. Two boats were set to accompany the aircraft on Thursday, but no further announcements have been made regarding potential findings.

Suthard explained that tubing is a “regular activity” in the area, including on the Dan River, however, riders are warned to stay away from the dam as it is “a pretty steep drop.”

Cates told reporters on Thursday that tubing is a common activity in the area but most people will get off the river and walk around the dam, as several signs mark the path. The 8-foot-tall dam is extremely dangerous authorities say the signs are very clear about the hazards involved.

Authorities are also wondering why it took so long for the four tubers to contact authorities when they got separated from the group, however, it’s likely they didn’t have their phones on them.