Wow, this lake! Gosh the color is CRAZY.
I love taking photos of places like this. It looks like I totally Photoshopped the thing but honestly I did not. The water really is that color, and it's gorgeous. I am still working through all the photos from this trip (and technically, I am still on the trip and taking plenty more).
Emerald Lake is about an hour from Banff (in the Canadian Rockies) and technically it sits in Yoho National Bank, not Banff National Park. Oh, and it's in British Columbia, not Alberta. Hope that's not confusing! :-)
Just Google it whenever you find yourself in the area and bring the camera. It's incredible.