The incident happened on Sunday afternoon.
Tragedy reportedly struck when a brewing storm caused trees to topple and fall on the teenagers while they were in the water.
“They were swimming in the river when there was a storm, a windy atmosphere that had uprooted some of the trees and they had fallen on some of them — those who were apparently swimming,” said a spokesman of the tourist site.
The Mail reports that the secondary school pupils were in a river close to Kintampo waterfalls on Sunday afternoon.
Kintampo waterfalls is a popular tourist destination in the Brong-Ahafo region of Ghana.
Ghana National Fire Service spokesman, Prince Billy Anaglate, described it as an “unusual incident.”
He said 18 students died at the scene, while two others died in hospital.
The spokesman added that 11 more were receiving treatment, including one of the school administrators in charge of the trip.
“We extend our condolences to the families of the dead and pray for the injured,’ said the country’s tourism minister, Catherine Abelema Afeku, in a statement.
Accidents ranging from deaths caused by mass flooding to petrol tanker explosions happen sporadically in Ghana because of lax regulations and disregard for rules, The Mail notes.