Common Darter

Thanks for the ID John.
I have often thought that he lagoons where this was may be brackish due to their close proximity to the sea - I'm sure some sea water gets across through the gaps in the bunds during storms at high tide.

The clues here are the way that the black edging the top of the frons does not extend down the sides of the frons, together with teh yellow stripe running down the otherwise black legs, a hint of antehumeral stripes and some black lines on teh side of the abdomen. (Southern Darter would have a similar frons but the legs and abdomen would look different.)

The pterostigmas are pale grey because this is recently emerged, also hinted at by the sheen on the wings. The pterostigmas will colour up later.