But Kenya's largest water tower has been under siege. Illegal logging, encroachment and settlement have scarred its once dense canopy. Streams have dried, wetlands are shrinking and what was once a green fortress is increasingly fractured.
Yet the rivers flowing from here, including Mara, Sondu, Njoro, and Ewaso Nyiro sustain millions downstream. They, too, power hydroelectricity dams, feed lakes Victoria, Turkana and Naivasha, and several water bodies as far as Narok and Nandi.
Athletics coach Charles Ngeno, who is also the chairman of the Nakuru County Coaches Welfare Association, sees the forest as inseparable from athletics excellence. He links the science of high altitude training to the Mau's unique ecosystem.
"The altitude here is already a gift for us. The trees make it (Mau) a power bank of oxygen. It releases clean and healthy air," he says.
"At high altitude, oxygen is scarce, and the body adapts by producing more haemoglobin. It is like a natural EPO (Erythropoietin) but unlike doping it is sustainable and honest. That is why athletes from here dominate when they run at lower altitudes."
"The Mau is not just a forest, it is a lifeline. It feeds our lakes, sustains our fans and powers our economy; we cannot afford to ignore it. The time to act is now," said Nakuru Governor Susan Kihika at the event.
According to Jeptha Rono, a public relations officer at the Athletics Kenya, South Rift region, they are targeting to register 3,000 athletes in the competition for 21km and 10km, and 5km and 2km fun runs.
Winners in the major races will pocket Sh350,000 and Sh100,000 respectively, where all top 30 athletes in both events will be awarded.
The marathon doubles as the launch of the Mau Forest Complex integrated conservation and livelihood improvement programme, a 10-year plan to restore the critical ecosystem.
The project targets to rehabilitate 33,138 hectares of the forest, fence 500km to stop encroachment, and bring 143,803 hectares of farmland under sustainable practices. It also hopes to enroll 200 schools in environmental education, with 10 model schools leading the way.