How to Obscure a Portion of a Map

[ArcmapUser]

New to GIS, ArcMap, AI, and graphic design in general so be gentle.

Working on a project and I have attached the exported image of what I have so far. The project is to show as much of the inundated area (the area that looks like water washing over land) as possible while obscuring everything else (obscure, not clip). The problem I am running into is that I cannot obscure the upper portion of the map without affecting the inundated area. I tried to transpose the colors so that the inundated area is dark but that affects the overall look of the map.

As I am new to this, I would prefer to stick with what I have, regardless of have elementary it may appear, instead of trying to get fancy. Any thoughts and suggestions would be greatly appreciated.

[DanPatterson_Retired]

what are the inputs to the map? a vector file? a raster file? an image?

If it is the former, double-click on the layer, go to symbology and change the dark blue color to something else an the roads to the same.

More information is needed, since changing colors in files can be real easy depending on the format

[DavidBarnes]

Maybe look into dataframe clipping?

[MichaelMiller2]

Another cartographic option might be to create a polygon mask and using transparency.  

[ArcmapUser]

Thank you all very much for your comments. I am changing this a bit. To give a bit of backstory, my project - in part - is to show the effect of Superstorm Sandy on Brooklyn, NY (Kings County). I have been working off of 2010 Census Tract shapefile of New York City (the five boroughs that make up New York City of which Brooklyn is one).

To make things easier and cleaner, I would like to find a Kings County (Brooklyn, NY) shapefile. I found a shapefile under the 2010 TIGER/Line® Shapefiles page but the map looks like an abstract design of Brooklyn. More specifically, it looks like the shapefile incorporates the water surrounding Brooklyn. Does anyone know where I can get a 2010 census tract shapefile of Brooklyn, NY (Kings County) that only contains the land mass? For those not in the New York metro area, this is what Brooklyn looks like:

Brooklyn - Wikipedia