The intergovernmental convention aims to combat the "increasing loss and degradation of wetland habitat for migratory waterbirds," and "wise use" of wetlands for the "benefit of humankind."
But Bundala is now losing a war against invasive plant species and the very nature of its water, which made it a haven for migrating water fowl, has changed.
"You cannot just declare a site as Ramsar and go to sleep," says Sarath Kotagama, a academic from Sri Lanka's Colombo University who is president of the Field Ornithological Group of Sri Lanka, a bird conservation group.
"A unique site has certain characteristics. If you want to preserve them you have prevent successional change.
"If you do not do something, a wetland will fill up and be reduced to a narrow area where water will drain."
Kotagama says wetlands are under constant 'seral' stage change. In a wetland, putrefying vegetation will settle at the bottom, create peat and eventually fill up.Bundala is in Sri Lanka's lowland dry zone, and is subject to flooding in the wet season. As the water dries up gradually, salinity increases, allowing a unique eco-system to grow around it.
Unlike forests, which also change, but much more slowly, a seasonal flooding and drying up cycle makes quick and visible changes in a wetland like Bundala.
But other forces are also at work in Bundala.
Drainage water from a large irrigation project in Lunugamvehera, which started in the 1980s, has flowed across the Bundala's Ambilikala lagoon into the sea, gradually taking the salt with it over the years.
Now in the rainy season, the already water-logged wetland gets flooded very quickly. New bird species that do not inhabit brackish water are now found in Bundala.
These include Purple coot and Moorhens. But the number of other waterfowl, including migrant ducks, terns and gulls may be falling.
"There are very little birds, more marshy-ness," says Kotagama. "Bundala was declared a Ramsar site with flamingoes. There were about 3,000 flamingoes visiting each year."
"We have made its water fresh and we have lost flamingoes," he says.
Only a handful of flamingoes are sighted or just heard in the night now.
Kotagama, a former head of Sri Lanka's wildlife agency, says when the site comes up for renewal under the Ramsar convention at the expiry of 20 years next year, the diminishing bird life will be a challenge for authorities.
Brackish water allows crustaceans that various waders consume - including flamingoes - to flourish.
"Years ago, kirri isso (a white hued shrimp) used to grow in the lagoon in the season when the lagoon opens to the sea," recalls Tissakuttiarachchige Ariyadasa, a villager who still herds buffaloes in the wetland.
"People from Malala village used to collect the shrimp and earn a good income. Now the price of a kilo of kiri isso (white shrimp) is about 500 rupees. But people can now catch only fish."
Ariyadasa cannot accurately recall when villagers last collected shrimp.
"By the time President Chandrika Kumaratunga came (in 1994) there were no shrimp," he says thoughtfully, as his buffaloes go splashing into the wetland leaving the tarred road.
"It was probably during president Premadasa's time that we last saw shrimp."
Kotagama says an attempt was made several years ago to dam the incoming fresh water and divert it for cultivation and then run off direct to the sea under a project supervised by the University of Colombo.
But the project fell through when an environmental organization went to court against the move.
Kotagama says Sri Lanka's authorities and conservationists have a heavily 'protection' oriented or 'hands off' approach, where an area is left undisturbed and without human intervention rather than active management.
Bundala was a 'sanctuary' when it was originally declared a Ramsar site. At the time Kotagama headed Sri Lanka's wildlife agency.
It is now a 'national park' and under tight protection. Parts of the original sanctuary which included inhabited areas, were dropped when the Ramsar designated area of the wetland was made into a national park, subject to stricter 'do not touch' laws.
But authorities have so far not tried to prevent villages like Ariyadasa herding buffaloes in the park.
The nation park is half of the original Ramsar declared area of the sanctuary.
"Conservation does not mean no human activity," says Kotagama. "Many Ramsar wetlands are teeming with human activity."
These include Lake Geneva in Switzerland which has ship traffic, and a salt pan in the middle of Tokyo which attracts an estimated 200,000 thousand birds.
Bundala village dates back to the time of Sri Lanka's ancient kings and the wetlands have survived with villagers' interaction until the ambitious irrigation works started up under then Sri Lanka president J R Jayewardene.
A key thrust of the programs at the time was to grow rice, a water intensive crop that grows under full inundation, which has irrigation run-off saturated in fertilizer and is close to the heart of Sri Lanka's politicians.
Other threats to the wetland are also literally growing each day.
All over Bundala national park as well as the Hambantota district in general, a species of mesquite (Prosepis juliflora), a native from the American continent is thriving and taking over arid land.
"Mesquite takes salinity from the soil," says Kotagama. "It was an introduced plant."
A species of cactus, Opuntia dillenii is taking over the rest of the terrestrial area of the park.
An attempt to destroy invasive plants in a section of Bundala's terrestrial area, with has not worked, with the plants coming back again as there has been no follow up work, says Kotagama. But physically destroying the plants is an expensive business.
There have no concerted efforts to commercialize the use of mequite which has found to be useful as a source of fuelwood and charcoal in other countries, including India.
"For years we had a protection regime," says Kotagama. "Now we have to re-think."
Unless active management comes, with invasive species on one side and fresh water contamination on the other, the Bundala national park, and its birds as well as its status as a Ramsar site, is facing an uncertain future.