Common Blue damselflies start flying a few weeks after the Azure damselflies and I've noticed that the Azures fly close to the water, but the Common Blues fly along the grassy paths, and they are the ones you will see flying all around your feet as you walk along the riverside. The male is shown below, and it is all over blue. The Common Blue Damselfly can easily be confused with the Azure Damselfly which is also blue.

Common Blue Damselflies start off a dull pink colour when they emerge, and slowly change to the bright blue - you can see this in the photo below...

The female Common Blue Damselfly can be blue, but is more commonly green, as in the one below. You can see that although the thorax (back) is the same pattern, the abdomen (tail) is not, having much less colour in the stripes, and lacking the double solid segments at the ip.

The main difference between these and the Azure Damselfly is the pattern on the thorax (back). With the Common Blue this is an overall blue area, whereas the Azure has more black areas, and a large half length black line (the coenagrion spur). You can see this clearly in the image below. These patterns may just look random, but are surprisingly consistent on all damselflies.