It looks like it could be an Abedus water bug. Look at it on google. I found one about 50 years ago on the Yuba River. It was so large, probably well over an inch with eggs all over its back, that I was afraid to touch it. I later found out that the males are the ones who carry the eggs glued to their back. They live in rivers and feed on other aquatic insects.
Yep, Robber fly. Think someone else had a picture of one a while back too. Come in all sizes and colors, my favorite ones look like bumble bees.