The tour group of seven people -- five Kenyans, a local tourist guide and a "non-resident foreigner" -- had been caught in the flash flood Sunday in Hell's Gate National Park.
"Six bodies of the flash flood victims have been recovered, leaving one tourist missing. The search and rescue operation continues as we reach out to next of kin to share details of sad incident and plan together next course of action," KWS on its official Twitter page.
Search and rescue teams had initially recovered two bodies on Sunday but four more were found as efforts continued throughout the night, KWS said.
A helicopter was dispatched from the capital Nairobi, which is about 100 kilometers (62 miles) southeast of the park, to help with search efforts on Sunday.
The gorge in the popular park was closed Sunday following the incident, according to the agency which said that tour groups were usually accompanied by guides, who are trained to detect storm water flowing down from the gorge and alert visitors to impending danger.
"Since the last similar tragedy in 2012, we have created clearly marked emergency exists along the whole gorge as escape routes in case of danger like the flash floods," KWS said Monday.
At least seven members of a church group were killed in a flash flooding while walking on a gorge in the park in 2012.
Hell's Gate is a popular hiking and cycling spot for tourists and locals and is known for its towering cliffs and gorges carved by a prehistoric lake.
The park's scenery inspired the 1994 Disney animation "The Lion King," and the 2003 film "Lara Croft: Tomb Raider -- The Cradle of Life" was shot on location there.