There were a lot of birders there today and of course lots of activity around the Dell. That's where I saw a flash of blue fly into the undergrowth at the edge of the water. None of the other birders with scopes set up were bothering to look at it. I'm assuming they had already seen it and were focusing on other more exciting birds- such as the pair of screech owls that have been reported at the Dell recently.
Here is where I first sighted him at the edge of the water. There was also a female cardinal there splashing around trying to cool off.
He then flew up into the bushes on top of the wall behind the Dell, where I got a better picture.