What are the locks in San Francisco Bay for?
Answer:
For many years the south end of the bay was used for evaporating salt. The area is divided into ponds by little walls (I think they're called dikes but I'm not sure). Sea water is let into one pond, and after it evaporates a bit and gets saltier it goes to another pond. Finally it ends up in a special pond with a very flat bottom where the salt is harvested by a sort of bulldozer that scrapes it up.
As the water grows more and more salty, little brine shrimp grow in it (they also grow in the Great Salt Lake). When it gets saltier still they die. Their little dead bodies make the water look reddish or brownish from the air, but it is not polluted or anything.
A few years ago they stopped the salt-harvesting operation. Now the area is being slowly restored to its natural state.
dry docks
shallow and dry were the first two clues. South San Fran Bay and the colours clinched it ... under the Dunbarton Bridge ... salt ponds.
You are seeing the old South Bay saltponds. They are interesting in that the trapped water is of different salinities...mostly all too salty for fish and most invertebrates but supportive of various single species (usually) of highly salt-tolerant (halophyllic) bacteria or algae. Thus the vivid and different colors from one pond to the next.
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