STEP EIGHT: HERE A LAKE, THERE A LAKE
There are many ways to add lakes & rivers to my map, all of them acceptable. I will paint them on top of the land in a new "Lakes & Rivers" layer. First I use a bright blue so they stand out & are easier to visualize. (see image below)
Remember (& forgive me if this seems condescending): Rivers flow from high ground or springs to the sea, not the other way around.
When all are drawn, I choose the Magic Wand tool, click anywhere on my blue, and the entire system of lakes & rivers is selected. I will keep this area selected for the next few steps.
From my Swatches I first select a light blue that corresponds with my oceans, then I use the Paint Bucket tool to fill the area.
Next I choose a slightly darker blue and quickly dab & draw around the lakes & rivers with a fuzzy brush at 50% fill. I do this again with a darker color, too.
Next I Filter>Artistic>Sponge the water, playing with the settings to somewhat match the sponging of my oceans. I repeat the sponge two more times.
Finally, I create a new layer above my Lakes & Rivers layer called "River Outlines"; then in that layer I Edit>Stroke the selection with a 2 px. black line. Now all my rivers & lakes are outlined.
I can Select>Deselect (Ctrl-D) now.
Hmm, I see two things I don't like:
1) the black outlines appear very harsh, so I will Filter>Blur>Gaussian Blur the River Outline layer at about .4px, just to take the edge off.
2) some of my rivers do not connect with the sea as well as I'd like, so in the River Outlines layer I clean them up with the eraser & a couple dabs of river color.
Below is the final image result!