Looks like the angle of the sunlight more than anything. First one the sun is in front of you, or directly above, and is skimming off the water, creating reflections that are hiding the color of the water. Also, the excess light hitting the lens is decreasing your exposure time and desaturating the sky.
The second one, you have turned a little and the sun is more behind you, so you aren't getting the reflection on the waters surface, and the sun isn't hitting the lens directly.
The filter, being out in front of the lens, could also be catching some sunlight and making things worse. Think about when you shield your eyes in direct sunlight to see better.
Overly white images, like bright beaches, or snow, tend to screw up exposures because your cameras meter is programmed to expose 18% grey correctly. When you have alot of white, it tends to underexpose and turn white things muddy. Always open up a 1/2 to a whole stop when you are looking at an image that is predominately light/white.
One more reason to shoot manual.