Ok, we just used our lasso to crop out the still water in our overlay, but we were not very neat and need to "touch" it up. The screenshot below will show some areas where we need to clean up.

Select the "Paintbrush" from the toolbar menu. I have it circled in the example. Make sure the controls palette is open and look at the example for the settings I chose for the brush tip. I generally use "round" for the tip, "1" for size, "marker" for brush tip, and 100 for the other settings. I'll use a larger tip size for bigger areas. Feel free to experiment with these options to what suits you. Before beginning to paint, make sure the foreground in the color palette (circled on example) is the same color as the area we cropped out. Use the "eyedropper" (step 2) if you need to change the color. The active foreground is the color that will appear on your "canvas" when you begin painting. Ok, let's start painting. If your image is small or if your eyes are as bad as mine, you may want to magnify, or zoom your image. Select the magnifying glass from the toolbar. It's the icon that looks like a magnifying glass and should be the second icon from the left. Left click your image once to zoom it in. Each left click increases the zoom even more and right clicking zooms it out. Once you're ready, select your paintbrush again. Use the left mouse button and start touching up the areas you missed with the lasso. Each click paints a pixel the size of the paintbrush. If you are brave, hold down the mouse button and drag your mouse for quicker painting. Do a little bit at a time, and check your image in normal size. I'd suggest saving your image every few minutes in case you botch it up. Trust me, it happens as this takes a lot of practice and patience. I touched up the above example so it looks like the example below...

Almost done! ... Save your image and let's move on to STEP 4 to make the final adjustment, change the overlay image to a transparent gif, and then put it all together.