Head back to your layers, then add a mask to the layer that contains your reflection. Alt (Option) + click on it to show the mask, then hit Ctrl (Command) + V to paste into it the contrasty version of your Blue channel. Deselect it, then use the Brush
to finish whiting out the water
and blacking out the foreground grasses. The foreground in this image is detailed, so I spent a few hours perfecting it using the Pen tool and the Quick Selection tool.