It is; unfortunately there's not much you can do with blown highlights. Next time you're up against this sort of situation, consider shooting it as an HDR, or perhaps look into the purchase of graduated neutral density filters.
you as a last resort could create a selection of the water in photoshop and adjust it independently. smooth it, soften it or change the color tones. The rest of the image would be unaffected. Blend the selection layer accordingly.