There are two waterfalls that can be found within walking distance along the Icefields Parkway in Jasper National Park. One of those is Athabasca Falls, pictured in this image. The falls are located about 18 miles south of the town of Jasper, and are known for the amount of water that quickly flows from the Athabasca River. There are a number of viewing platforms where visitors can get close and see (and hear) the speed and force that is generated.
I stopped here as I made my way from Banff to Jasper. I had taken about three shots when the heavens opened up and I headed back to my car. Undeterred, I returned the next day when the weather improved. I knew that to capture the falls properly, long exposure was called for. I popped on a 6-stop ND filter and began photographing. When trying to get the "right" exposure to get that silky smooth effect, I would suggest experimenting with the aperture. It is more of a hit or miss approach but if you take enough shots with different apertures, you will get one that works for you. Don't rely on your camera's LCD screen--just experiment.
I processed this in black and white as I find these type of shots look better, especially when there isn't a lot of color anyway. For the best look at the image, look at it on a black background by clicking on the photo.