A member of the group who survived the deluge, Ivraj Singh Hayer, 31, said his relatives “started going one after the other”.
His wife and five other family members died – including two children. A family group of 13 had travelled from Nairobi and the western city of Kisumu for a weekend away.
Although it had begun to drizzle, they decided to visit Hell’s Gate National Park’s gorges after tour guides told them it was safe.
Authorities say, however, that rainfall can build up in surrounding areas and rush through restricted spaces.
Mr Hayer said the water “came from nowhere” at about 3pm, and when he phoned reception he said “the guide next to me shouted, “tuna bebwa na maji” (“the water is carrying us away”).
When water began rushing through, some of Mr Hayer’s family jumped to one side, while others were swept away.
“The guide was trying to save my nephew and they both slipped and were swept away by the floods,” he said.
“For more than an hour the rest of us held tight before the water subsided and we managed to walk to safety.”
A man stands a section of the gorge at Hell’s Gate National Park
Five of those who passed away were Kenyans of Indian descent. There was also an Indian national and the driver, who was Kenyan.
Their bodies were found 30km (19 miles) away, the Kenya Wildlife Service (KWS) said.
It added that it was “holding counselling sessions with the bereaved to help them cope with the untimely deaths of their loved ones”.
Gorges in the park, which has been used as a location for movies including Tomb Raider II:Cradle of Life, are prone to flash flooding,
In 2012, seven members of a church group were killed while trekking.
KWS said the gorges had been closed indefinitely because of “ongoing rains in the region”.
