I think you may be thinking of a CICADA.
It's not a dragonfly nymph, but rather a closer relative to the water boatman and backswimmer (fact!)
They are widely distributed throughout the north and south island and make an appearance during the hot dry summer days as terrestrials that fly/fall into the water. They have an amazingly high pitched sound they emit.
There are some very good imitations around.
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