An Indonesian court has rejected a lawsuit that sought to stop a hydroelectric dam project that campaigners say will result in the extinction of rare Tapanuli Orangutans in the Batang Toru rainforest.

The US$1.5 Billion project in the heart of North Sumatra's rainforest is expected to be completed in 2022.  The area is also home to agile gibbons and Sumatran tigers.

"Where they are building the dam is actually where the density of this species is the highest, so it's actually the worst area in the forest you could build it," said Professor Serge Wich, a specialist in primate conservation at Liverpool John Moores University.  He was one of the scientists who confirmed the existence of the Tapanuli Orang which was only discovered in 2017. 

"There are many other potential places in Indonesia to build the dam.  It's unclear why this has to built here," Wich said, "The dam will put the orangutans on a firm path to extinction."

The environmental group the Indonesian Forum for the Environment (Walhi) had brought the suit against North Sumatran officials, only to have it stopped in the Medan State Administrative Court.  The Chinese firm Sinohydro will build the dam with financing from Bank of China.

"As Batang Toru's main financier, Bank of China could pull out and stop the dam from being built," said Walhi executive director Dana Tarigan.  "Primary forest is currently being cleared for the dam and scientists have documented orangutans fleeing the area.  Time is running out fast."