From the name of it I thought it would look different 
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No comments on the map? Not even a "nice map" ? What type of comment was this... but yes, I was originally picturing separate islands dispersed throughout the map.
On the sides, it fades to black too quick. Can barely tell there is water on the sides.
Make the polygon shading for the shadows a little more gradual and not so definite.
This comment can be disregarded: who would dig a tunnel under a lake? The ceiling would collapse on your head, especially since it's dirt and sand.
