Moruya teacher Will Douglas has been fined $1200 after locking himself onto machinery in a rail corridor for Queensland's planned Adani coal mine.
His protest using a home-made steel device began at 6.30am on Wednesday and he remained locked on until after lunch.
An ambulance treated the former Greens candidate for the state seat of Bega for dehydration and police took him into custody at about 1pm.
Queensland Police said they used cutting tools to unlock the device.
He was charged with obstructing police and placing an immobiliser on a vehicle (wheel clamping). He pleaded guilty to both charges in Mackay.
Ten anti-coal activists were alongside Mr Douglas during the protest.
Frontline Action on Coal member Andy Paine said Mr Douglas had been with the group for the past three weeks.
"Will has been up here for about three weeks, being a part of our community and helping to work against construction of the mine," Mr Paine said.
"He has been really great, someone with a lot of experience, skills, knowledge and a level head."
Mr Paine said it was over 30 degrees on Wednesday and conditions were "tough".
"I think he deserved a cold drink after it," Mr Paine said.
"Will was very keen for people to understand that climate change is an issue that affects us all - we are in a climate emergency and have a desperate need to take action.
"He was also very keen to stress that Australian people working together have the ability to act on climate change.
"Often the government and media portray protesters as being a fringe group or out of touch with reality - Will is a farmer, biologist and teacher.
"He understands and reflects the diversity and those who are against the action of this mine."