need to reproduce a picture effect

[Deanpeddle]

hi ... first of all I am a GIMP newbie and trying to figure stuff out on my own with YouTube and tutorials.  Here's what I need help with: I screen captured a couple of map locations using google maps.  The first attachment is a section of a map that is close to what the original looked like. 

I then did a bunch of edits and changes to get the look in the 2nd picture. Notice how the water is represented in a "fading away" (no idea what the effect is called) blue on each side of the highway.

Here's my problem: I have another map and would like to reproduce the water in the same way but I can't figure out how I did it!!?!?  anyone have some suggestions?

[Blighty]

Summary (will need some refinement eg around the road)

1) Add a white layer below map layer
2) On map layer use Colour Select to select blue water
3) On map layer add a layer mask - initialize with white
4) In mask - bucket fill selection with black
5) In mask - stroke selection with white (about 20 to 30)
6) In mask - Gaussian blur to suit
7) Select > None

[Deanpeddle]

(10-20-2018, 06:43 AM)Blighty Wrote: Summary (will need some refinement eg around the road)

1) Add a white layer below map layer
2) On map layer use Colour Select to select blue water
3) On map layer add a layer mask - initialize with white
4) In mask - bucket fill selection with black
5) In mask - stroke selection with white (about 20 to 30)
6) In mask - Gaussian blur to suit
7) Select > None

OH my god!!! thank you Blighty... I had to google some of the lines of your instructions but once I understood them (and just a tiny bit of trial and error) it worked PERFECTLY!!! (I didn't need to use line 5) 
thanks so much

[Delfin93]

Could you post your result here?