Orford Castle used to be on the coast until the Orford Ness spit formed
Havergate Island celebrated its 60th anniversary as a bird reserve in 2008, but coastal erosion means time will soon run out for Suffolk's only island.
The RSPB-owned reserve lies on the River Ore - in between the spit of Orford Ness and the rest of Suffolk.
"The best guess is that the island has 30-50 years," said site manager Aaron Howe.
"Even if Havergate breaches, it's envisaged it'll turn into salt marsh, which will still be used by birds."
Havergate Island is a collection of saline lagoons surrounded by an earthbank and is a haven for once-rare wading birds - most noteably the avocet which is the RSPB's symbol.
Aaron said it's essentially a man-made construction: "500 years ago this site was walled and it was farmed for a very long time - right up until the RSPB took it over in 1948 after avocets appeared there in 1947.
Havergate covers 108 hectares and access is via boat from Orford quay
"It was also used for gravel extraction and you can also see remnants of the old farmhouse. You can still see walls and tiles near what is now our tractor shed."
The six lagoon areas offer vital habitats for birds away from humans: "Avocets are now doing incredibly well nationwide, so we still get up to 800 avocets passing through in the autumn.
"In the spring we're getting more lesser black-backed gulls, herring gulls, common gulls which are all relatively scare worldwide, so the Alde/Ore is quite a key site for them."
When BBC Suffolk visited the island, there was a volunteer in residence. Lesley Davis had come from Rugby to spend a week carrying out repair and painting work and counting birds.
RSPB volunteer Lesley Davis in one of the volunteers' chalets
"It's very nice to be in such an isolated, special place and to have it all to yourself is a unique situation," she said.
"I walk around and enjoy the peacefulness of the place. It's nice to be away from traffic completely and just really the natural sounds of the birds.
"The sea lavender's out at the moment, there are butterflies as well as birds. I've been painting the huts, fencing and counting the birds.
"I've been here a couple of times before so I've seen the avocets but this time there are a lot of spoonbills which are stunning to look at because they're so large."
Retreat of the land
Havergate Island covers 108 hectares of which 60 hectares is saline lagoon, 40 hectares saltmarsh and four hectares vegetated shingle.
Although the RSPB is celebrating Havergate's birthday, it knows the island has a limited lifespan. Rising sea levels mean the island is likely to disappear, or at least be washed away, at some point in the 21st Century.
Aaron Howe: "We did knock a hole into one compartment to the north of the island to monitor the changes that would take place as part of the managed retreat back to salt marsh.
"Even if Havergate breaches, it's envisaged it'll turn into salt marsh, which will still be used by birds, rather than saline lagoons.
"The RSPB would then create saline lagoons on other reserves along the Suffolk coast."