Ecological threads and activities described on-line Snail keeps the spring water clean. http://www.pbs.org/saf/1204/teaching/teaching2.htm
river flow change: Beaver, Otter, Muskrat
The Colorado River is shared by many in the arid region of the southwest. The Hoover Dam being was built in 1931. Dams are intended to provide safety from raging floods and protect cities and farms from drought via their massive stores of water. Unfortunately the redirected water has changed river habitat and impacted fish and wildlife. Efforts are currently underway to restore damaged habitat and boost the population of these creatures.
http://www.water-ed.org/coloradoriver.asp about frogs
http://allaboutfrogs.org/weird/general/raining.html each of the animals of the southwest in this story can be studied.