The US$3.6 billion (115 billion baht) dam along the Irrawaddy River was supposed to export about 90% of the electric power it generated to neighbouring China, but President Thein Sein's government ordered it suspended in 2011, saying it went ''against the will of the people.''
Now, many in this nation of 60 million - which only recently emerged from decades of military rule - worry construction will resume after the 2015 general elections.
Waving banners calling for permanent cancellation of the Myitsone dam, around 60 people gathered early Sunday in a suburb of the main city of Yangon.
They will walk along the Irrawaddy, passing through towns and villages to raise awareness about the project, said Ye Htut Khaung, one of the organisers. He expects the march to Myitsone in Kachin state, where the dam is located, to take up to 70 days.
The vast majority of Myanmar do not have access to electricity.
Environmental activists have said the dam would displace countless villagers and upset the ecology of one of the country's most vital national resources, the Irrawaddy. It also would submerge a culturally important site in the ethnic Kachin heartland, where the Malikha and Maykha rivers meet.
''Everyone knows the natural surroundings of Myitsone can be destroyed, but they keep doing the project anyway,'' said Ma Phyu Phyu, one of the marchers.