Surrounded by rich fishing grounds and fertile land, Angkor - the epicentre of the great Khmer empire - prospered. But in the fifteenth century the empire collapsed, leaving only ruins of temples behind.

The reasons why are still unclear, but many believe that the Khmer people simply ran out of a crucial resource - a problem which led to the collapse of many other great civilizations.

This week's Earth Report discovers how the mistakes of the past are being repeated today - both in Cambodia and across the world. This is a story about how abusing our natural resources can cripple our future. It's a story about the need to assess the value of our natural assets so they're available year after year forever and not destroyed by those who want to take the money and run.

Easy money: here today, gone tomorrow

Cambodia's brutal 30 year civil war is over and the country is basking in a new found prosperity. But this prosperity may well be short-lived. Overpopulation and corruption have put enormous pressure on once-abundant wetlands and forests - two of Cambodia's most prized and profitable natural resources. Overfishing and deforestation is destroying these ecosystems to such an extent that Cambodia's future may soon repeat ancient history.

Overfishing: profit and loss

The Tonle Sap is not just any lake, it's the largest body of fresh water in South East Asia and one of the most productive inland fisheries of the world. But this once-overflowing fishing basket is under threat.

The floating village of Kchong Kneas is one of 25 fishing villages on the Tonle Sap where people live an extremely poor subsistence lifestyle entirely based on fishing. For years the fish harvest has decreased in quantity and quality, and some species of fish have even disappeared - a clear indication of overfishing.

Recently the government divided almost 80% of the lake into profitable 'fishing concessions' for which wealthy businessmen pay the Cambodian government $200,000 per concession. Separated from these privately owned concessions by bamboo fences, subsistence fishermen have access to only a small part of the lake. As a result, both local fishermen and wealthy businessmen are put under pressure to overfish - one to make ends meet and the other to reap a profit on their initial outlay.

But Tonle Sap's troubles don't stop there. Next, Earth Report finds out how widespread deforestation is not only destroying Cambodia's rainforests, but is threatening the very existence of the lake.

Banking on the forest: cash for timber

Between 1980 and 1995, Cambodia lost 27% of its precious tropical rainforests mainly through commercial logging. The effects of widespread deforestation have already had an immense ecological impact on the lake. The resulting soil erosion is causing the lake to silt up. At present rates the Tonle Sap could be completely silted up by 2025. Already the lake is becoming shallower every year. And as the lake silts up, valuable fisheries will die and a whole new series of ecological breakdowns will arise.

Some say that corruption is the main cause of environmental degradation in Cambodia. Cambodia's forests have long been regarded as a private bank account - funding wars, coups, political parties and business interests.

On top of commercial logging, the forest is also cleared for fuel and to make way for rice and lotus agriculture - an income-generating activity for many Cambodians.

But tightening of reforms in forestry may not be the answer. Businessmen who lose out to forest conservation policies may move their activities to the Tonle Sap, increasing pressure on the lake's resources. Clearly there must be another answer.

Ecological economies: valuing nature's resources

For years Cambodians learned to live on a day to day basis not knowing what the future would hold. Although times have changed, this prevailing thought pattern still holds true today. This, coupled with Cambodia's new era of peace and prosperity, has fueled rampant economic short-terminism and put Cambodia's natural resources - the very source of their income - under threat.

These problems are not particular to Cambodia but are found the world over. As population increases on our planet, natural resources, if not used sustainably, will be depleted. Yet, people carry on tapping into their decreasing natural resources like lemmings racing towards a cliff. So what will happen when we eventually run out of water, timber and fish? Only the fate of our ancestors highlights the seriousness of the issue.

The hard truth is that our economic system makes it difficult for us to look after our planet the way we should. Clearly priorities need to change. In our global economic system, conservation of natural resources needs to have a market value in order to encourage governments to use these resources in a sustainable way.

For this reason, the United Nations Environment Programme and economists aim to assist the Cambodian government in assessing the true economic value of the Tonle Sap if used in a sustainable manner.

Conserve or collapse: the choice is ours

Every major civilisation has eventually collapsed. In the past, the effects of those collapses were contained within small parts of the world. Now the problem is far greater. Local economies are intricately interconnected with our global economy. And if we continue with the same processes that led to the collapse of civilisations of the past - the problems we'll be facing tomorrow will be global, not regional.

Cambodia's future depends entirely on how government officials will implement and apply conservation policies. And to do that means evaluating the true worth and cash value of their natural resources. But Cambodia's problems are merely a microcosm of the problems facing governments across the world. Every nation has a duty to understand the true value of their natural resources and sustain them for the sake of humanity.