Is there anything more gorgeous than white puffy clouds reflected on a body of water? Especially at Rivers of America, I imagine Walt himself looking over the water out to the Mark Twain sailing by.
For these two photos I set up my tripod along the river and took two different exposures. One standard exposure, with the water as you would see it in person. Rippled glass and sharp reflections. For the second shot, I used an neutral-density filter. That basically puts a dark tint over the lens which cuts all light wavelengths, allowing you to use a slow shutter speed (leaving the shutter open longer) without overexposing the photo. Over the course of the long exposure, the water is moving constantly and becomes blurred in the exposure, giving it that smooth matte-finish look.
Long exposure is a common practice for night photography, allowing more light into the lens and achieving effects like light trails, but during the day it can be used to achieve smooth water movement and cloud movement.