Since 2013 activists and local tribes in Malaysia's Sarawak state on Borneo island have blockaded jungle roads leading to the proposed dam site on the Baram river.
They say decades of government-orchestrated logging and dam-building have led to social and environmental disaster.
With elections in Sarawak expected within weeks, activists said the state government had sent them a letter stating that plans to forcibly acquire necessary land had been revoked.
"The struggle to resist the proposed Baram dam has finally paid off, because now the dam is scrapped."
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That could not be immediately verified, however.
Sarawak Chief Minister Adenan Satem was quoted by Malaysian media a year ago as saying the dam would go ahead. No government statement was immediately seen.
The dam would have flooded an area half the size of Singapore and was part of a controversial state government drive to use hydroelectric development to spur economic growth in one of the country's poorest regions.
Authorities had previously declared plans for around a dozen dams, saying Sarawak must tap its massive hydroelectric potential to provide power for hoped-for investment in a nascent industrial sector.
Three dams have already been completed, at Batang Ai, Murum and Bakun, and have become lightning rods for criticism.
Activists say they will provide far more power than the state needs, and have destroyed fragile ecosystems and uprooted tribes that had made their homes in the rainforest for thousands of years.
The dam-building spree was launched by Sarawak's former chief minister Abdul Taib Mahmud, who stepped aside under a cloud in 2014 after 33 years in power.