Its Nik Software, not Nikon. Its a plugin to complement the Photoshop CS5 and adds a ton of effects for all fields you love to shoot.
Neutral Density (ND) filters allows you to control the light going through the camera even when shooting at mid day. You can also delay the shutter speed depending on the number of stops or how dark the filter is. The higher the number, the darker the filter, the longer your exposure. Gradual Neutral Density (GND) filters are commonly used in landscapes to control the exposure on a part of the photo, in your case, the sky and the water. There are many uses of these filters and if you are going to shoot landscapes, you shouldnt leave home without them. One of the best ND is the B+W brand. For GND, I recommend the Lee brand. If its ok with you, I could post your photo processed on Nik Software.
Cheers and warm regards from Manila
Mel