The first turbine is spinning, electricity is pulsing out, and the water level is climbing in the Borneo jungle behind Malaysia's huge $2.2 billion Bakun hydroelectric dam.

But questions continue to swirl around the viability of a project described by critics as a graft-plagued human and ecological disaster -- and as opposition mounts against a dozen other planned dams in Sarawak state.

The first turbine from French giant Alstom began producing electricity in August and the dam's reservoir in the Malaysian portion of Borneo island has swelled to the size of Singapore since impoundment began a year ago.

After years of warnings about the impact on Sarawak's pristine jungles and the forced removal of thousands of local tribespeople, the dam's head Zulkifle Osman sees light at the end of the tunnel.

During a tour of the facility, the managing director of Sarawak Hidro who has overseen construction since 2000 defended the dam despite an electricity surplus in the state and the lack of a market for its power.

"It is a chicken-and-egg game," Zulkifle told AFP.

"I am confident there will be a lot of demand for electricity in Sarawak."

But dam opponents say the situation confirms warnings about Bakun as an ill-planned and unnecessary boondoggle.

The facility is located on the Balui River, a mighty waterway that drains a vast rainforested area of northern Borneo -- home to orangutan, spotted leopards, rare plants, and a renowned biodiversity.

The project was first approved in 1986 under then-premier Mahathir Mohamad as a cheap electricity source for more-developed peninsular Malaysia even though the country is a net oil and natural gas exporter.

But in a 2005 report, anti-graft watchdog Transparency International termed the dam one of the world's "Monuments of Corruption," citing years of delays, ownership changes, and overall costs that more than doubled.

"No users have made any legal written commitment for the usage of the energy," said Elli Luhat, a former Sarawak forestry official, now an environmental activist.

"I have a real fear that Bakun dam will one day become a white elephant."

Tribal residents say warnings about the dam's ecological and human impact are coming true.

Residents living in the shadow of the dam, one of the world's highest at 205 metres (673 ft), say the river's biodiversity has degenerated, fish catches have plunged, and once-clean waters smell foul and are unsafe to drink.

Silting has occurred, inhibiting navigation in the river, natives say.

Climbing into his boat in Uma Nyaving village about 10 kilometres (six miles) from Bakun, Kayan tribesman Richard Let complained of the thinning fish numbers.

"Now there is not enough for my family and the fish are small. The river is choking under silt and is making it difficult to fish with our boats," said Let, 31.

Downstream from the dam, nearly 12,000 indigenous Kayan, Kenyah, Ukit and Penan people live in traditional wooden longhouses in a resettlement area in the town of Sungai Asap. Their ancestal homes are now underwater.

They enjoy amenities unknown when they dwelt in the forest -- piped water, electricity, schools, Internet access and health services.

But Bulan Merang, 43, who moved to Sungai Asap 12 years ago, struggles to feed her eight children amid high food prices and new social strains.

"Children no longer respect their elders. Even my 21-year-old son says I am a useless woman whenever he gets drunk," she said.

The tribes, who previously grew rice and bananas and hunted wild boar, say their new land is infertile. Age-old hunting grounds are submerged and they must purchase staple foods.

"We were not dependent on money (before). Here everything is money," Bulan added.

Ironically, Sungai Asap's electricity comes not from Bakun but from a huge diesel-powered generator -- the dam's electricity is sent away on power lines criss-crossing the green terrain, headed to a state grid already at capacity.

Sarawak is rich in natural resources but poverty is rampant. Its leaders are keen to diversify from mining, agriculture and forestry and into high-tech industries and say ample power sources are needed to lure foreign investment.

"I am confident the power from Bakun will be taken up. MITI (the Ministry of International Trade and Industry) is working hard to get investors," Zulkifle said.

Zulkifle brushed aside concerns over the safety of Bakun, one of the world's largest rock-filled embankment dams, calling it "sound."

He said released water was treated to ensure it was clean and denied corruption allegations.

"All the money that is paid is audited. We are scrutinised," he said.

The dam was meant to help cut Malaysia's dependence on oil and gas for electricity generation. Up to 90 percent of output was to be sent to more industrialised peninsular Malaysia via undersea cables.

But economic downturns over the years forced protracted construction delays and shuffling of contractors, and the cable plan was shelved on cost concerns.

The Malaysian chapter of Friends of the Earth says nearly a quarter of electricity capacity in Sarawak already is unused, noting that the country as whole also has an electricity surplus.

The planned eight turbines will have a capacity of 2,400 megawatts when installed by 2014. Current Sarawak demand is 1,000 MW.

Then-finance minister Anwar Ibrahim suspended the Bakun dam and other big schemes in 1998 amid a regional financial crisis, angering Mahathir, who was known for backing grandiose projects.

It was revived in 1999 after Anwar was ousted in a falling-out with Mahathir, with Sarawak Hidro acquiring the project from original private Malaysian developer Ekran.

The dam's capacity remains far too much for Sarawak and only the undersea cable could salvage its viability, said Anwar, now opposition leader.

"Otherwise we will have a white elephant. Sarawak does not need all that power," he told AFP.

Despite the Bakun controversy, the state has plans for a dozen more dams, angering local tribes.

There are about 200 cases in Malaysian courts brought by indigenous people fighting state acquisition of their land for dams, timber concessions, or other developments.