(BIVN) – Rainbow Falls State Park was teeming with police and fire rescue activity on Friday, as another swimmer went missing in the deadly Wailuku River.

Four people went swimming in Rainbow Falls Pond in the early evening, the fire department said. One of them, a 20-year-old male, seemed to be fatigued and went underwater without resurfacing.

When rescue crews arrived, the three other swimmers were back on shore, unharmed and in no distress. Chopper 1 deployed rescue (scuba) divers and searched in the area where the missing swimmer was last seen.

The search was called off due to darkness, and will resume in the morning, the fire department says.