This is a not-great picture of an amazing effect that happens on the #SanFranciscoBay in certain conditions, where the different directions (?) and/or speed of currents in the water creates two-toned colors with that sharp line dividing them.
This was seen in a small park area next to the SF Bay, right after a big renovation. This refuse container was taller than me and wide and FILLED to the top with oyster shells that had been cleared out of the bay during reconstruction of the area.