At the age of 45, environmental activist Sasin Chalermlarp admits that embarking on the most physically gruelling mission of his life is ''not fun at all''.
STEPPING UP: Sasin Chalermlarp, left, and a fellow Seub Nakhasathien Foundation activist on their gruelling walk from Nakhon Sawan to the capital.
The Seub Nakhasathien Foundation secretary-general began a 388km march from Nakhon Sawan province to Bangkok last week to protest against what he says are rushed and potentially dangerous plans to construct a dam in Mae Wong National Park.
''If people think I am crazy, it would probably be a good thing,'' Mr Sasin said after finishing the third day of his long journey. ''I hope that from my madness, people will start to question why I am doing this, and they will find out more about my intention to oppose this dam project and to protect Mae Wong.''
Mae Wong National Park comprises nearly 900 sq km of pristine forest land in Nakhon Sawan. The park is part of Southeast Asia's largest remaining forest tract, known as the Western Forest Complex, home to Thailand's first Natural World Heritage Site, the Thung Yai-Huay Kha Khaeng wildlife sanctuaries.
Mr Sasin said parks like Mae Wong provide safe regeneration and recovery areas for endangered species.
The Mae Wong dam project has floated on and off the government's agenda for years, but was dusted off again after the 2011 floods as part of the 3.5-billion-baht water management scheme.
The Office of Natural Resources and Environmental Planning and Policy (Onep) is now pushing to complete an environmental health impact assessment for the dam so it can begin construction.
While the government claims the dam would help control flooding in the Central Plains region and provide irrigation to about 300,000 rai of farmland, environmentalists strongly oppose it, saying it would pose a major threat to the national park and the wildlife inhabiting it.
Recent camera-trap studies by the Wildlife Conservation Society and the WWF suggested the tiger population has been expanding inside Thung Yai-Huay Kha Khaeng and is spilling into neighbouring ''buffer'' parks, including Mae Wong.
The groups are demanding Onep halt its impact assessment of the dam.
The Seub Nakhasathien Foundation, along with several other environmental groups, submitted a letter opposing the project to Onep on Monday.
But Mr Sasin, who says his years as an activist have taught him that letter submissions achieve little, decided to take the protest a step further and embark on his march to raise public awareness.
''I think besides submitting a letter, we need to do something symbolic to demonstrate our strong will to protest against this project,'' Mr Sasin said.
''Mass rallies are one way, but considering that we have only a small number [of supporters], I think this walk can be as affective as any demonstration.''
The 45-year-old admits the physical element of his march is daunting, but said it is designed to highlight his organisation's dedication to the cause. ''To walk a long distance is not fun. People who can walk such a long distance must have a very strong intention to send a message to the public, which is why I chose this form of protest,'' he said.
Mr Sasin said he didn't have much time to prepare for the challenge, as the government was rushing to begin construction on the dam. Carrying only a few T-shirts, a few pairs of sports trousers, and two pairs of shoes, Mr Sasin will cover 388km before finishing his journey at the Bangkok Art and Culture Centre.
Along with 10 fellow activists, Mr Sasin has been walking under a mix of harsh sunlight and pouring rain. They begin in the early morning and end in the evening, covering about 30km per day. The activists seek refuge in temples.
The first two nights passed without incident, but Mr Sasin said opposition to their quest has begun to emerge _ some local organisations which support the dam project have blocked them from staying in temples in their areas.
Mr Sasin said he is unfazed. The only thing he thinks of is finishing the march.
''The rest is for the future to decide, as we have done our best,'' he said.