The team was en route to the Worcester base after battling a blaze in the area on Sunday night.
The truck lost control due to the wet roads, according to municipal spokesperson Jo-Anne Otto.
Reynhard, 55, was declared dead at the scene, while two reservist firefighters, Heinrich Matthyssen, 29, and Corbin Cupido, 20, were admitted to a local hospital for observation. Cupido was discharged later that evening, while Matthyssen was kept for observation.
Reynhard was an experienced firefighter who joined the CWDM fire division in 2003.
CWDM mayor Helena von Schlicht said: “This is immensely sad news. The loss of a firefighter at any time is tragic, however this loss has occurred so early in our fire season, which officially started on November 1. This passing brings into focus the danger that our firefighters face daily.
“On behalf of our council and fellow colleagues, we extend our deepest condolences to the family and friends of Colin Reynhard, who made the ultimate sacrifice.”
His death comes weeks after Working on Fire (WoF) pilot Nico Heyns was killed when his helicopter crashed while battling the fires in Vermaaklikheid in the Garden Route region.
The devastating Garden Route fires claimed eight members of a family in Farleigh last week.
The fires have been raging for 13 days with close to 90 000 hectares destroyed.
More than 400 people had to be evacuated from their homes.
Co-operative Governance and Traditional Affairs Minister Zweli Mkhize extended his condolences and acknowledged the firefighters, disaster management officials, and other emergency personnel “spending sleepless nights” battling fires, evacuating vulnerable people, and rescuing those “who are helpless” and at risk amid the raging fires in the Western Cape and Eastern Cape.
Hundreds of Working on Fire Free State firefighters and management arrived in the Garden Route region to help with mop-up operations and to relieve exhausted colleagues who have been battling the wildfires in different parts of the area.
Fire authorities said if cool temperatures and rainy conditions continued, they might be able to contain 80% of the fires in the region.
The Garden Route District Municipality said firefighters were still working to contain the blaze in Jonkersberg, between Mossel Bay and Oudtshoorn, and in the De Vlugt area, about 40km inland from Plettenberg Bay and Knysna.
“Additional resources have been sent to attend to the hot spots at Noll, Kransbos.
“Aerial resources cannot be used due to low visibility. The precautionary evacuation of the Diepwalle and Kransbos communities will remain in place until it is confirmed that the area is safe,” the municipality said.