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In ancient times, Er’hai lake in Yunnan, China was known as Xi Er’he, Yeyu River, Yeyu Pool, Er’he, Kunmichuan and Kunming Pool. Legend has it that people began to live near the lake after the hot sea cooled and marine life started to grow. It is said that Er’hai came into being after a volcano eruption spewed lava and rocks. The mouth of the volcano closed to form a pot, and water filled this pot. Then, organisms began to appear.

The ancient volcano calmed down and left what is known as Ximatan – a water pool at the mouth of the volcano with hot springs in the surroundings.

Scenic Er’hai, the seventh largest freshwater lake in China, is in the watershed of three big waterways: the Lancang-Mekong River, Jinshajiang River and Yuanjiang River. It has a catchment area of 2,565 square kilometres and a water surface of 253 sq km. It is 41 km long and three to nine km wide. The average water depth is 11 metres, with the deepest being 22 metres. Its total water volume is some three billion cubic metres.

Emptying into Er’hai lake are 117 large and small rivers, including the Miju River and the Poluojiang River and 18 lesser rivers at Cangshan. It flows out into the Lancang River, which is how the Mekong’s upper reaches are called in China, through Yangbihong. Water in Er’hai comes mainly from melted snow and rainfall.

Er’hai is home to 34 species of fish, two species of shrimps, 50 plant species (there were 61 in 1986) including seaweed and eel grass, and 192 species of planktons, principally of the Bacillariophyta, Chlorophyta and Cyanophyta families.

But Er’hai was threatened by an explosive growth of Cyanophyta in October 1996, which resulted in a drop in the transparency of lake water from four metres to 0.5 metres. The water soon had a nasty smell, forcing people to fetch mountain spring water from afar. Another such growth of Cyanophyta took place in 2003, when water quality during the months of July, August and September dropped to Grade IV.

“You must protect the water in order to live on it,” people here say. Without Er’hai, there would have been no Dali.

Worried by the deterioration of their lake and its water, the people of Dali city, near Er’hai, demolished houses that were built too close to the lake, returned the land they had reclaimed from the shore, stopped breeding fish in ponds, and restored the original lake, forests and wetlands.

They also launched six major projects for the protection of Er’hai. These involved ecological restoration, pollution control, control of rivers that flow into the lake, refuse collection and sewage water treatment in urban areas, water conservation in the catchments, and environmental protection and management education.

These drastic steps yielded some improvements. According to a 2005 report by the Dali Environmental Education and Management Station, Er’hai showed much better green indicators. It met Grade II standards in the Environmental Quality Standards for Surface Water for three months and Grade III standards for nine months (on a scale from Grade I to V, with I being the least polluted).

The water of Er’hai gradually became clearer after two years of hard work. Water transparency reached nearly two metres, and total phosphorous (TP) and total nitrogen (TN) levels dropped significantly.

By December 2006, the average water quality was Grade III and water transparency was 1.52 metres. The integrated index of eutrophication (a process where bodies of water are oversupplied with nutrients, leading to excessive plant growth) was at the middle level. The main pollutant was TN, exceeding standards by 75 percent.

Still, the pollution of Er’hai had been placed under control.

WHEN WATER DRIES UP

For generations, the people of the lakeshore village of Shacun have drunk water from Er’hai and the Wanhua stream, which runs through the village. Shacun, under the administration of Xizhou town of Dali city, is not far from Xizhou, but is rarely visited by tourists.

A tablet erected by the neighbourhood committee of Ranyi Lane of Xizhou Town describes the quality of water in less-polluted times: ‘A clear and clean stream runs through the village from west to east. Before 1958, all families fetched water from the stream to drink and for use in washing. On the evenings of July and August of the lunar calendar, boys tried to dam up the water to catch fish and eel.’

But the villagers stopped drinking water from Er’hai in 1988, after an acute gastroenteritis epidemic broke out. The water level in wells dropped, along with the quality of water, that had turned muddy and was no longer potable. The Wanhua stream almost dried up, and did not flow at all during the dry season. In many ways, it became like the 17 other streams from north to south whose flow had become erratic as well.

To solve their problem with drinking water, Shacun’s residents spent 720,000 yuan (95,000 U.S. dollars) to lay a six-kilometre pipeline at the foot of the Cangshan Mountain in Dali to lead up to the water extraction pool and water storage pool on the upper reaches of the Wanhua stream.

But the following year, the people had to rebuild it and spent another 450,000 yuan (59,382 dollars), because they had to pay the residents of Wenge village, located at the water source, for using their land for water supply lines. The elders of the two villages mediated the dispute between the upper and lower communities of the Wanhua stream, and fixed the fees to be paid.

After that, it seemed drinking water would no longer be a problem for Shacun village. But trouble arose once more in mid-2006, when the water extracting pool and part of the pipeline were destroyed by landslides caused by rains and the operation of a small power station built by Wenge residents. A visit to the area in November 2006 showed that repairs were still ongoing.

CORE AREA

Aside from being a source for drinking water, Er’hai is the core area of the Canshang-Er’hai national natural reserve and is a national scenic spot. Its presence helps regulate the climate, provide industry and agriculture with water and maintain biodiversity. It is the foundation for a sustainable social and economic development in the whole catchment area and even in Dali prefecture.

Some 720,000 people live in the Er’hai catchment area. Around it are the two urban districts of Dali and Xiaguan, 10 townships, including Xizhou, Haidong and Shuanglang, one provincial economic and technical development zone, and one provincial tourism zone.

The Gross Domestic Product of the area in 2002 was 8.057 billion yuan (1.06 billion dollars), 51 percent of which was Dali’s.

Data indicate that Dali prefecture received 6.5 million domestic tourists in 2005, 11 percent more than the previous year, and 172,000 tourists from overseas, 27 percent more than the year before. Total tourism income of the prefecture accounted for 16 percent of its GDP in 2004.

But with urbanisation and the rise in the living standards as well the increase in tourists comes a corresponding increase in, and demand for, water consumption.

The Dali Water Supply and Drainage Co plans to use Er’hai and mountain spring water to supply drinking water to local residents. It will start from Xiaguan before expanding to other areas, allocating two water taps for each household.

But this plan does not seem to address the fundamental problem of Er’hai’s deteriorating water quality. And although no one living near Er’hai, surrounded by water all around, wants to have to source drinking water from elsewhere, they may soon have to accept this fact.

LIKE ER’HAI, TONLE SAP IN TROUBLE

The Tonle Sap or ‘Great Lake’ downstream in Cambodia, fed by the Tonle and Mekong rivers, is believed to be where the Naga, the mythical seven-headed serpent of Budhist lore, lives. The lake, the largest body of freshwater in South-east Asia, is the lifeline of Cambodians.

Thousands of kilometres of fertile black soil surround the lake. Tall mountains and great rivers on the Central South Peninsula extend from north to south, forming a fertile alluvial plain.

The Tonle Sap has the unique feature of changing with the flow of the rivers around it. Phnom Penh, the Cambodian capital, lies at the confluence of the Tonle River and the Mekong River. During the dry season, from November to April, the flow of the Mekong River goes down, and water from the Tonle Sap replenishes the Mekong via the Tonle River. The Tonle Sap, in turn, decreases in size to about 2,500 square kilometres. But during the rainy season, when the Mekong River’s water levels are high, the Tonle river reverses its flow and swells the Tonle Sap. Water is pushed up from the Mekong into the lake, increasing the lake’s size to a massive 16,000 square kilometres and flooding wide swathes of fields and forests. For fish, the floodplain is a rich breeding habitat.

About 62 percent of the water in the Tonle Sap comes from the Mekong, and the rest coming from the Tonle basin. From July to September, about 300 million cubic metres of water flows into the Great Lake.

But although water feeds life in this part of South-east Asia, the lake communities still do not have enough clean and safe water to drink. Only 35 percent of Cambodia’s 13 million people – 65 percent of urban residents and 26 percent of rural folk – have access to clean and safe water.

If Er’hai in China is changing, so is the Tonle Sap.

Five years ago, the residents of Kompong Khleang could drink the water from Tonle Sap. Today, it can only be used for washing. Villagers had to change the roofs of their houses from corrugated tin sheets to palm leaves so they could collect rainwater, which is then stored for use during the dry season.

The Tonle Sap is polluted by human and animal discharge, sewage water and emissions from motorised boats, and is being encroached into by agricultural expansion.

Data from the Mekong River Commission show that the nitrogen content of the Tonle Sap, an indicator of pollution, is lower than that of the Mekong River. Some say, however, that the lake’s pollution has been underestimated.

One thing is clear though -- the Tonle Sap plays a tremendous role in regulating the ecology of the Mekong River, which flows from its headwaters in Tibet down through Yunnan, Laos and Burma, Thailand, Cambodia and finally Vietnam, where it reaches the South China Sea. Without the massive body of water that is the Tonle Sap, the pollution of the Mekong would be even worse.

Dissolved oxygen (DO) is another indicator of water quality. For fish, a dissolved oxygen level of 5-8 milligrammes per litre or at least above 4 mg per litre is best. A slight lack of oxygen may not kill the fish, but it slows their growth. Excessive DO content would cause gas bubble disease in fish.

Data show that the DO content of the Tonle Sap is 2.2-7.8mg/L. Generally, water with DO content less than or equal to 3mg/L is categorised as Grade IV.

DO content usually rises in August. Although the month falls during the rainy season when water flow is heavy, pollutants are also washed into the lake. The poorer-quality water of the Mekong River also flows into the Tonle Sap. It is at this time that the ecological absorption effect of the Tonle Sap in the whole Mekong River basin reaches its peak.

Another major indicator of water quality is pH value, which measures acidity and alkalinity. For freshwater fish, the proper pH value is 6.5 to 9. The average pH value in the Tonle Sap in April is 6.6 and reaches a high of 7.2 in September.

Many factors, including the destruction of vegetation as well as population pressure, account for the drop in the water quality of the Tonle Sap. But overall, it is excessive development on the lake that is to blame.

A MIX OF THREATS

In the 1960s, the Tonle Sap was protected by one million hectares of flooded forest. Thirty years later, the flooded forest area had shrunk to 600,000 hectares, due largely to massive felling of trees for use as firewood or for sale. The land cleared of trees was planted with rice to meet the locals’ needs.

From 1996 to 2000, Cambodia’s agricultural output increased at an average annual rate of eight percent, basically achieving self-sufficiency in grain. Its rice output in 2000 was four million tonnes. In 2001, the government set the goal of exporting 500,000 to 600,000 tonnes of rice by 2005.

With vegetation reduced and more land used for purposes like agriculture, wildlife also decreased, leading to lower biodiversity and the shrinkage of the Tonle Sap. Siamese crocodiles have almost disappeared. There are 149 known species of fish in the Tonle Sap, but another 17 species are on the verge of extinction. These include the spotted billed pelican, the stork leptoptilos dubius, the houbara bustard Chlamydotis undulata and the grey-headed fishing eagle.

There are five species of tortoises in the Tonle Sap. In 1985, two adult Batagur baska were collected by the Fishing Administration Department of north-western Siem Reap province from local fishermen who had picked them up from the lakeside mud. According to elderly locals, a small number of Batagur baska was seen in the early 20th century. Today, researchers say there is no evidence that the Batagur baska still live in the lake.

Fish and rice are part and parcel of Cambodian culture. The Tonle Sap, which provides 80 percent of Cambodians’ protein consumption, has the biggest fish production in the world of about 230,000 tonnes of catch a year. This is equivalent to more than 50 percent of the total catch in the country and accounts for16 percent of Cambodia’s GDP.

The fish live in the flooded forests, which are crucial for breeding, before the lake reverses its flow.

During the Norodom era from 1851 to 1904, there were laws restricting fishing and banning the use of unlawful fishing gear that contributed to the extinction of fish species. A fishing zone was demarcated in 1929. By 2000, the Cambodian government had cancelled 56 percent of these zones.

Since 2006, the government has imposed fishing bans from March to November with the intent of looking after the long-term health of the Tonle Sap system, given local communities’ dependence on it. The fishing season starts after the Water Festival, which is held to mark the reversal of the waters of the Great Lake in October or November, depending on when the waters reverse and flow back into the Mekong River.

But poaching remains a problem and the use of illegal fishing gear and methods, including poison, electricity and trawl nets, persists.

There is also concern about the heavy fishing of water snakes, which are used for food, as feed for crocodiles and are also in demand in overseas markets such as China. The number of crocodile farms around the Tonle Sap has been increasing over the past 20 years, pushing up demand further. An adult crocodile can consume one to three kilogrammes of snake meat daily.

People in Fucun village use spiked nets to catch various types of snakes – usually the rainbow water snake, Tonle Sap water snake, striped water snake and puff-faced water snake. Statistics show that in 2004 and 2005, four million snakes were caught, making the Tonle Sap the biggest source of water snakes in the global trade.

ONE WITH THE LAKE

Most people living around the Tonle Sap continue with their traditional way of life in harmony with nature. Living in houses on stilts or in fishing boats, they seem to have become one with the Tonle Sap, integrating the lake into their lives.

The water people raise and catch fish, plant vegetables and raise pigs. They build thatched huts right over the water, or half-leaning against the land. These huts usually have a veranda on both ends: one is used for leisure activities and the other leads to the kitchen and toilet. There is a pigpen on one side of the house or a small piece of land for planting vegetables. Under the hut and on both sides of the waterway, there is plenty of hyacinth, which is fed to the pigs.

More than 4.5 million people live in the Tonle Sap basin, and of this, 1.6 million live around the lake.

The population is growing at a rapid 4.6 percent a year, a trend attributable in part to early marriages and early births. More than 40 percent of those living in the Tonle Sap basin are under 14. At the same time, many are moving to the cities in the hope of finding jobs in sectors such as tourism and construction.

Tourism contributes four percent to Cambodia’s GDP. Tourism in Siem Reap, where the Tonle Sap also flows through and the majestic Angkor Wat complex is located, has developed so rapidly that it has left water supply and drainage development far behind. Since the drainage system in the city proper is inadequate, the environmental protection department has asked all hotels and restaurants to build their own sewage treatment pools, but only a few have done so. Hotels and restaurants often extract underground water to meet their needs.