Need advice on making this map all entirely black and white (no gray)

in above image, trying 2 things cannot figure out:

 

1. make dark blue rivers black (the ultimate goal remove them).

2. large bodies of water used cyan color, while replace color tool changed of water white, along coasts of these landmasses there still anti-aliasing of various shades of blue/cyan remaining. these parts white.

 

i have tried use replace color tool , color selection tool used previously, cannot work these parts. advice appreciated. thank you.

hi andrew,

there multiple ways depending on want. 1 simple option open current photo in photoshop. click adjustment layer icon , select threshold adjustment layer.

that make every pixel go either black or white.

then take slider , move right remove thinner white lines in rivers. see screen grab.

that 1 quick way - may remove of coast line edges depending on want.

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