Yes, water is one of those things which has a reflection which varies depending on the angle you view it at. At shallow angles like you get when stood on the bank it picks up a significant amount of sky. When viewed from above then you see deeper into it and it looks a lot darker. The sea is naturally a blue / green as well as that from the sky so any light which does go into the sea and reflects back from particles will appear with a blue green tint to it. Fresh water is less like that tho and I think just more clear in nature so it just steadily goes to black as it gets deep. I am less sure about this tho.

If you want high res pics of coastline thats not the US but are 100Mb is size then the ones from Linz in new zealand are a good start:

click on the coloured squares on the map:
http://www.linz.govt.nz/topography/a...geo/index.aspx

Like this:
http://www.linz.govt.nz/topography/a...s29/index.aspx

Don't try to look at the full res ones in a browser - 200Mb TIFF is gonna kill it. You need to right click download them. Even the JPGs are pretty huge as well. But these are great reference pictures and they have a reasonable usage policy for them.