|The Nile at the Aswan High Dam, which has dramatically altered the course and flow of the ancient river. (Source: NASA via Wikimedia Commons)|
It shouldn't be a surprise - bad news tends to come in threes. In this case, the three problems are: water security (the ability to ensure adequate water supply for a population), poverty, and threats to biodiversity. A recently-published research study in Nature (unfortunately behind a paywall) maps threats to water security and freshwater biodiversity. It has found that places with poorest water security and most threatened freshwater biodiversity overlap. That's easily understandable, because when water or land is a scarce resource, humans will engineer a way to protect their own interests. The richer the country, the better they are able to do so, and therefore affluent countries have relatively high water security. However, the methods they use - such as dams, diverting rivers into canals - put biodiversity at threat, therefore affluent countries (such as the US and in Europe) also have high threat levels to freshwater habitats.
They also point out that water issues do not respect national boundaries. Damming a river will affect human populations both upstream and downstream, regardless of what country they live in. The same applies for fish and plant populations, for example. Therefore, they propose that conservationists and policymakers should consider the watershed as the basic level of analysis, and not just individual rivers or tributaries. In the case of great rivers like the Amazon, these watersheds can be on the level of continents. Doing so will help to balance immediate human needs with the long-term stability of biodiversity and ecosystem health, which in the long run will benefit humans by the maintenance of ecosystem services.