It was winter, and quite chilly. And it was dark (but I repeat myself). Jane and I were walking the docks, enjoying the ambiance, when we noticed that there was a large patch of water between the docks, perhaps 100 feet across, that was gently glowing blue.
It was almost as if there was a light source under water, filtering up. Several other folks had noticed it too, and we all stood there, watching it, talking quietly as if to avoid disturbing it. But after a while, we all wandered away. After all, it really wasn't doing anything... it was just sitting there softly glowing, pulsing a little, slowly.
The next day that patch of water was completely unremarkable, and we haven't seen the effect again.