Very true. I guess the challenge is to balance, if it's at all possible, the needs of humans and/or other species with that of the overall ecosystem. For example, in India there is a massive program underway to connect the various rivers across the country to alleviate drinking water shortages and increase the use of inland waterways for transportation. However, the net ecological impact of the program is not known. I doubt it is possible to really calculate, in advance, the impact of such programs.