Assistance on compositing lakes of specific shapes onto terrain in aerial photos.

Find one of the foot shapes and stamp it down.  Make it a reasonable size  — 300 pixels maybe.

Copy the layer, and drag to the new path icon in the path panel

Find a brush preset with a rough outline.  Maybe add a tiny bit of scatter to make it rougher if needed.

We are going to stroke the outline of the foot , so size the brush accordingly

Right click the path you made earlier, and chose Stroke Path.  Simulate pressure needs to be turned off.

Merge the foot print and stroked outline layers tofgether, and define as a new brush preset.  

Stamp down your new brush, and in Layer Styles give it some Inner Glow.

Inner glow is normall used with bright effects, but we are repurposing it here because, unlike Inner Shadow, the effect is applied equally all around the layer.  So we need to change blend mode from the default (Screen) to multiply.

Otherwise, edit for best effect.

You know, I am looking at the last screen shot, and thinking that the outline is not as jagged as I expected.  This is what the preset looked like, and stamped on a plain white background, that's how it stayed, but we are losing some of that roughness on that rocky background. 

Perhaps search Kyles Mega Pack using Rough.  Adjust hardness way up, add some scatter, and drop spacing to about 30%

I think you could do a bit better with so experimenting.

If you want to make footprint lakes in the 2nd image, you could add the footprints from the Shapes panel (Window > Shapes), load them as a selection (Ctrl (Windows)/Command (macOS) + click the thumbnail of one shape then Shift + Ctrl/Command + click the thumbnail of the 2nd), and add a prompt in the Contextual Task Bar (Window > Contextual Task Bar) for "pools of water" or something similar until you get a result that you like.