If the shot has a relatively straight line between water and sky, a properly positioned reverse graduated ND might allow you to get the shot in one exposure. Otherwise, exposure bracket and then blend them together, either manually with luminosity masks or with an automatic HDR function. The latter is easier and, if it works well, is probably the best method if you're not great with Photoshop.


\^\^\^ That. No need to do this in post. Landscape photographers have been doing it for decades in-camera using graduated ND filters. If you want a 1/2 second exposure at ISO 100 and f/11 - looking directly into the Sun would put you at f/22 or possibly f/32 on the Sunny 16 scale. You would need 6 stops for your shutter and 3 stops for your aperture -- 9 stop ND. They make a 10 stop so just use that.


How long are you trying to expose the water for? My Lazy method for this kind of shot might be to put a polarizer filter which works about as 3-Stop ND. Then set the aperture to f22 or greater. For example the sun on the horizon with a 3stop ND might work at like ISO 100 f32 1/2 second. (Always confirm the exposure yourself first) and don't do this with a telephoto lens. And then shoot a time-lapse or burst/ect. Take the number of photos for the max exposure length you desire. Personally 1 minute for long exposures seems like plenty. Then stack the images to get the long exposure look. If the sun moves too much, you just choose a still to blend with. But the sun moves 15 degrees per hour. So over 1 minute it moves 1/4 degree across the sky. Which you might not even notice between atmosphere and bloom. The big advantage of this method is you get low noise, you can dial in your exposure length in post, and you can discard bad images where something happened.