No, this isn't 'Attack of the Giant Caviar' in the making, it's actually 400,000 little black balls covering the surface of the Ivanhoe reservoir.
There were found to be high levels of bromate (a carcinogen that forms when bromide and chlorine react with sunlight) in this reservoir back in 2007, and when the Department of Water Protection became aware of it they began constructing a new underground reservoir in Griffith Park. However, while it was being built they had to figure out a way to keep the sunlight out of the water.
Now go and make yourself a nice bromate-free cup of tea. You deserve it.