The Danube Delta was once just a shallow sea cove. But about 6,500 years ago, it began filling with silt. The result is one of the largest and best preserved of Europe's deltas -- a paradise for nature lovers and scientists. It's a complex ecosystem, which serves as a filter for the Danube River and is home to many rare species of wildlife.

The water, the life force of the delta, is everywhere. Besides the three important branches of the Danube that flow through the delta, there is a maze of large and small lakes, rivulets, channels, sand banks, marshes and reed beds covering more than 5,500 square kilometers. It's a dynamic system, actually growing by about 30 meters a year. Its unusual micro-climate system has even given rise to several small areas of tropical forest.

The Delta Danube was declared a protected biosphere reserve in 1990 and one year later, UNESCO put it on its list of World Heritage sites.

The Delta is a huge bottleneck for the waterbird population

The mixture of land and water, reed beds, willow trees and location make it an ideal place for birds. Millions come here to rest and eat during the migration seasons, or to have their young. Ornithologists have recorded 325 species of birds here.

"It's the greatest wetland of Europe," says Alexandru Doroshenku, a local scientist who works on issues such as biodiversity. He adds that it's also one of the most important roosting areas and migration spots for the birds.

"The Danube Delta is a huge bottleneck for the waterbird population from northern Europe and eastern Europe," Doroshenku says. "The Delta is a vital place for all those populations. If the Delta would disappear next year, you can be sure that all those populations probably would disappear, too."

The Delta is a naturalist's dream

Much of the Danube Delta is almost inaccessible. There are comparatively few roads. The best way to experience it is to meet the Delta on its own terms -- on the water.

Floating down the channels and river branches by the reed beds, one can catch sight of several endangered bird species, like the red-breasted goose, the Dalmatian pelican or the pygmy cormorant.

"The Delta is this paradise, this dream for every naturalist," says Pavel Simeonov, a Bulgarian naturalist who first visited the Delta 25 years ago. "Anywhere in Europe, there are many reserves, but you always have these landscapes, wind farms or big roads." In the Delta, these disturbances are non-existent.

The Delta's population is part of its diversity

While the Danube Delta is a naturalist's Nirvana, it has been inhabited for centuries. Today, there are about 15,000 people in the Delta, many of them traditional fisherman who appear to live lives seemingly untouched by modernity.

Shepherds lead flocks of sheep around. Some of the more isolated villages still lack electricity. Horse-drawn wagons are a common mode of transport.

"The people are so well adapted to this environment that you feel they are part of it and they don't disturb it," Doroshenku says. "If you see an old fisherman with his boat, you feel that he belongs to this place, is part of the landscape and is part of the diversity."

Tourism increasingly threatens the Delta

While the traditional inhabitants are well integrated into this fragile ecosystem, newer arrivals sometimes are not. The jumping off place for the Danube Delta is the city of Tulcea, with a population of some 92,000. It's here where more and more people are coming to experience the region and that has some people worried.

Orieta Hulea from the environmental group WWF coordinates its lower Danube green corridor project. She says the Danube Delta is a very important tourism resource for Romania and will be developed in the future.

"The point is how can we be sure that we will still have the natural values of the Delta together with the development," Hulea says. "This is the crucial point to keep the balance between development and nature conservation."

Pollution needs to be kept in check

The Danube Delta has survived several ill-advised projects. During the communist era, Romania's dictator Nicolae Ceausescu, although he was a hunter and fisherman, thought the Delta was "too wild" and needed to be tamed. His regime drained swamps, marshes and lakes and transformed the areas into agricultural fields. The government forced traditional fishermen to become farmers. It proved disastrous for the people and for the environment.

As Mother Nature often does, the Delta is bouncing back. After communism fell, the drained areas were re-flooded and have begun coming back to life.

"This is a lesson that we should learn something from," Doroshenku says. "In the future, this will not happen again."

But some things scientists or the government can't control -- such as the pollution that flows into the Delta. Many of the impurities that enter the river from its source in Germany and along its meandering route through eastern Europe end up in the Delta. It acts as a giant filter of sorts, cleaning the water before it enters the Black Sea. But if pollution levels climb, it could have an effect on the wildlife that depends on the Delta for its very existence.

Still, researchers are cautiously optimistic that the Danube Delta has a healthy future ahead of it, if politicians maintain and enforce laws that protect it. Structural funds from the European Union once Romania becomes a member state could also help, says Hulea. To her, the Danube Delta is one of Romania's natural treasures, one of the few places left in Europe where one lose oneself in the pure majesty of the natural world.

"I can tell you that it's the most magnificent place on earth," Hulea says. "You are amazed from the first step. You feel the power of the nature around."

Something as special as that, she says, deserves to be preserved for future generations.