The problem of disappearing seagrass was first noticed some years ago on the northern side of the Port and is now impacting the southern end.

There are differing theories as to why the seagrasses, which once flourished and are so vital for the sustainability of the Port's unique marine life, are in decline.

The problem according to Don Payne, a prominent campaigner and fisherman from Pindimar, lies with the dumping of sand into the waterway, which makes its way into the Port's estuary, lakes and river systems.

"Unfortunately, events were ignored in Port Stephens for many years," he said.

"They have now unfolded with a devastating effect [on] the ecosystem and marine life including razorfish, green weed crabs, periwinkles, blood worms, green nippers, drift oysters, mussels and fledgling fishes."

The problem now spans both sides of the Port - from Swan Bay, Myall River, North and South Pindimar, Tahlee, Karuah to Tanilba Bay, Mallabula Point, Lemon Tree Passage, Tilligerry Creek, Cromartys Bay, Soldiers Point, Salamander Bay and Corlette.

"In my lay opinion, building developments on the southern side of Port Stephens which occurred around 1990 started to change the water hydrology," Mr Payne said.

"The large sand bar across the entrance into Port Stephens is now virtually gone allowing large swells in a south-easterly direction to go unimpeded towards Jimmy's Beach.

"Replacing of sand has been going on since the 1980s, but in the last three years the seagrasses have been disappearing."

With five generations of oyster-growing in Port Stephens, Robert Diemar from Nelson Bay fears the seagrasses will be wiped out before too long.

"The problem is a combination of factors ... the sand movement is one reason, another is the increase in the number of native black swans," Mr Diemar said.

He believes the swans, virtually non-existent on the southern side a few years ago, have migrated from the north after that area was ravished of all its seagrass.

Both men believe that unless governments begin working alongside fisheries and interested parties the health of the Port's most alluring tourist attraction will deteriorate.

At the time of publication the Examiner had not received a statement from Department of Primary Industries on the issue.