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That looks very nice! It can be difficult to shoot long exposures of water without the water then starting to blow out with all that white. You did good here it looks like, and yeah, the D800 sure helps with it's great DR to make these shots a lot easier.
Something else to try if it's a bit on the brighter side, is to use the Multiple Exposure mode and take 4 or 5 shots in a row. With the moving water, using ME can let you take multiple shorter length shots and it overlays them so that it looks like one longer exposure. It's not perfect, but it's a nice alternative to a single long exposure.