MANILA (AFP) - In Spanish colonial times, the Pasig river that snakes through Manila was the linchpin of the transport and commerce network in the Philippines.
But in the aftermath of World War II, rapid population growth, urbanisation and industrial activity slowly destroyed it. Today, when the capital's 12 million residents flush their toilets, the waste water ends up in the river.
Former leader Joseph Estrada, looking across the Pasig from the majestic 18th-century presidential palace on its banks, once called it "the country's largest septic tank". In some spots, the dark water looks like porridge.
Frustrated with the horrifying state of the 27-kilometre (17-mile) river, Estrada ordered a 15-year project to clean it up by 2014 -- and hopefully see fish return to its now filthy waters.
Backed by 176.8 million dollars from the Asian Development Bank (ADB), the project entails the redevelopment of riverside slums, relocation of tens of thousands of squatters and the launch of a passenger ferry.
At the halfway mark, government officials and ADB experts say progress has been made, but much more needs to be done if the Pasig is to regain its former splendour.
"The pollution level has improved since 1990," insists Zoilo Andin, deputy director of a public-private river rehabilitation commission and a senior official at the government's Environment and Natural Resources Department.
The volume of waste water is indeed down by six percentage points from 17 years ago, he notes. But downstream from the presidential palace, men naked from the waist down can still be seen relieving themselves by the water's edge.
Andin says the government is well aware of the uphill battle it faces, noting: "President Gloria Arroyo is the number one customer of the filth and smell of the Pasig. She lives there."
Cleaners fish out some 200 tonnes of solid waste every day though the actual amount dumped daily could be nearer to 1,000 tonnes, the official says.
With just 10 percent of Manila covered by a sewerage system, an ADB study estimates that the river basin is vulnerable to leaching from 1.1 million household septic tanks.
In addition, half a million squatters live on the banks of the Pasig, according to the ADB survey, producing most of the municipal waste that flows into it.
More than 6,000 families have been moved to affordable housing projects, and the slums have been replaced by parks and greenery, but ADB sanitation specialist Paul van Klaveren says that is insufficient.
"Does the project reduce pollution to the river? Not really because although you are pushing people away from the river bank, pollution still goes into the Pasig," said Van Klaveren, who is checking whether the ADB money is well spent.
A ride on the new ferry launched in February, which links Manila's Makati financial district to the old walled city of Intramuros, reveals the problems facing those trying to save the Pasig.
Both river banks are lined with oil depots, construction sites and huge slums. Garbage floats in the murky waters, storm drains flow directly into the river and rusting half-submerged barges block the boat's path.
The ferry crew includes a diver who often goes down with a pruning hook to unclog debris -- ropes, mosquito nets, even mattresses -- from the propellers.
Not surprisingly, most of the 150 seats aboard the air-conditioned catamaran are empty.
"We are using the ferry boat as a platform for advocacy," Andin says simply.
While many of the factories on the banks of the Pasig have migrated elsewhere, high-rise housing complexes have taken their place, most without liquid waste treatment facilities.
The government estimates 65 percent of the pollution comes from domestic waste, with the rest industrial or floating debris.
The World Bank is funding a related project to build sewage treatment plants and employ mobile septic pumping trucks, but these handle only a small amount of the waste water that ends up in the river.
Andin admits restoring the water quality in the river remains somewhat of a pipe dream given current resources, as the project "does not attack the sources -- the tributaries and the open sewers."
But he says despite the shortcomings of the initiative, work must be done on the Pasig "to establish the credibility of the government and the project itself."
For Van Klaveren, "enforcement of the law is the more critical issue" in Manila.
He says China is "doing much better" with a similar project to clean up the Yangtze River, adding: "The same thing could happen in Manila but there should be a willingness to do that."