The Southern Hawker or Blue Darner (Aeshna cyanea) is 2.8 inches long and breeds in still or slow-flowing water. The nymph feeds on aquatic insects, and has been called the 'Great White Shark' of your local creek. It ambushes tadpoles or small fish in its quest for metamorphic growth.
This adult male was photographed in my backyard after I saved it from becoming dinner for European Garden Spider. The Darner catches insects on the wing, males often flying some distance from water as they patrol their territories. You may have seen two clash in the air. These confrontations are not unlike World War I air battles above the trenches!