Oval object fades away into blue sky.At approximately 15:00 on July 17 2016 we were getting ready to leave Boulder Lake campground in the Mt. Hood National Forest. We were observing hundreds of insects buzzing overhead and trying to discern what kind they were. (Mayfly species) Skies were crystal blue, no clouds. Occasional airplanes with contrails overhead were observed throughout the day.While looking at the insects flying directly overhead, I noticed a strange object out of the corner of my eye, away from the main group of insects. Turning to look, I observed what appeared to be an oval or egg shaped object as it quickly dissolved into the blue sky. Edges of the object were not hard to my eye, but clearly something there. Maybe a halo. Object then proceeded to disappear, or fade, very quickly into the blue of they sky. There was no perceived lateral movement.Direction would have approximately S/SW, but very high due to trees.I took pictures of the insects, but failed to take a picture of the object as it happened so fast. I stayed for quite a while trying to see if it would reappear. It did not.There were no jets, or contrails overhead at this time. This was also away from the main body of insects overhead and appeared to be at a great distance in relation to the tops of the trees overhead and insects.There was no sound. Total length of observed time was less than 10 seconds.I was the only one who saw it in our group. I was a little stunned and didn't say anything to anyone at the time, waiting to see if anybody else saw anything. Nobody did, however I was the only one in the group looking in that direction at the time.I'm an avid outdoors person, and am familiar with most types of aircraft and cloud formations, though not an expert. It certainly could have been some kind of atmospheric phenomenon that I am unaware of. It was odd, and not something I've ever observed before.