Harbour master Robert Smith said he had noticed increasing numbers of the lightweight, free-flying aircraft, whose pilot sits in a harness suspended below a fabric wing, similar to a parachute canopy.
But this weekend, he said one flew dangerously close to moored boats and frightened a number of birds away from their nests.
“What they are doing is irresponsible and dangerous, and it is unlawful to disturb nesting birds – particularly the terns,” he said.
“Yesterday (Saturday) we had one which was weaving in and out of the yachts on the quayside and virtually landed on one of the masts.
“It is a problem all along the coast and we need to identify these people in order to educate them.
“No-one wants to spoil their fun and I don’t want to be a killjoy, but we just want them to take more care.
“There are lots of fields and open spaces in Norfolk where they can do this, and they don’t need to do it over the marshes.”