Possibly the reflection from the sky?

The first thing to ask when color issues arise: is your monitor calibrated? Also, if shooting RAW, have you calibrated your RAW converter as described here? If the answer to either of these questions is no, then address that before proceeding further. If you're shooting JPEG, chalk it up to the camera jazzing up the color for you without your knowledge or consent.

In two locations this year I've had rivers in the shot come out looking unnaturally blue. It's a beautiful, deep blue, but looks "too perfect" to be real, like too much saturation. Once was in Cook State Park on the Kenai Peninsula in Alaska, and again recently at Snake River Overlook in Grand Teton National Park. The conditions were similar, though: an hour to two after sunrise with the sun almost directly behind me under clear sky. Is this a common optical effect I should be aware of? Is there a shooting fix? I wasn't using a polarizer. Once was with a Canon S70 and the other with a Canon Rebel XT, both RAW, both using around 28mm "equivalent" focal length. Unfortunately I don't have a place to post them on the web quite yet for you to see them.

Next time, maybe try turning down the saturation in the camera.

Im not exactly sure how it works, but cant you also adjust things like that afterwards since you shot it in raw?

The camera might be enhancing the image as digital cameras usually do. They seem to make things more colourful than they are, turning down saturation might help.

Can I see the pic? Its probably pretty cool how it is

If the rest of your colors are accurate, then I can say with near-certainty that the blue was due to the sky being reflected in the water.

Using a polarizer would have removed or reduced the reflection, giving the water truer color.

--Chris Nicholson
NicholsonPrints.com, NicholsonSports.com

At the risk of being pedantic is it blue? In some shots that I have taken it was more cyan A colour shift? try the dropper in PS to accurately measure the colour

One of the photos in question is the Snake River from Snake River Overlook in the Tetons, shot in raw with a Canon Rebel XT using the 17-85mm lens. The river measures red around 60, green around 65, and blue around 105 with the color dropper. In ACR I have the saturation set at 0, no calibration adjustment, exposure 0.

Just desturate your blue to taste. (?) Wow - now theres a problem I wish I had!

Adjustments layer: heres a couple ways to do it (there are others):
1) Saturation-Blue, or
2)Selective Color-Blue. Piece of cake.
Watch your greens if present!
Do any curves, etc. first, and put this adjustment layer on top while in 16-bit. Flatten, save as, sharpen to output, convert to 8-bit.

View it in your working color space, i.e. do not view sRGB in Adobe RGB color space unless you like cartoon colors

Paul