This sort of thing is right down my ally.
I worked as a junior researcher for a study done by the University of Lethbridge for the Alberta Ingenuity Centre for Water Research in 2004-05. (You can read our anual report here
http://www.albertaingenuity.ca/forms..._2004-2005.pdf)
Climatic changes in the foothills and mountains in Montana are having a big effect on the St. Mary tributary alone. The river is fed by snow from that region and almost every year since 2000, there has been less and less. Lack of dynamic fluctuation of lows in all 3 tribs of the S.Sask Basin are destroying the riparian communities as well, which is leading to increased suspended sediment in the water. The Oldman is so low in some areas that you can literally walk across areas of the river that just a few years ago were under several feet.
The Milk River (not part of the S.Sask Basin) is also in dire shape, and is important to agriculture in both Montana and Alberta, and is destined to become a hot political issue again in the near future.