The snow and ice stored within this resplendent arc of nearly 50,000 high-altitude glaciers are vital sources of water for the major rivers of Asia. GlacierWorks is a non-profit organization that vividly illustrates the changes to Himalayan glaciers through art, science, and adventure.
At this point, this is a classic example of trophic cascades. Sort of the "peppered moth" of the subject. This is a nice video about it. (I now see that the video has been shared already, but this also has an article (which includes the correction of deer/elk)
This is a great activity that can be adapted to any major river. I have done this with students of all ages. A great way to introduce Non-Point Source Pollution. I have used this demonstration with all age groups and it has a powerful impact.