A flock of great crested grebes floats on the sea, gently bobbing up and down under the warm November sun.

Every so often a bird dives below the surface, searching for a tasty morsel from among the 260 species of fish, crabs and shellfish that live there.

A little closer to shore sits a flock of greater scaups, freshly arrived from their summer breeding grounds in Russia. When winter comes, there will be about 25,000 water birds here at Kasai Kaihin Park, which was last month designated as a wetland of international importance, also known as a Ramsar Site.

Can this really be part of Tokyo?

“You can see how close the big city is to this place of nature,” said Tomohiro Sakashita, director for marine parks planning, waterfront development division, at the Tokyo Metropolitan Government’s Bureau of Port and Harbor, as he cast an eye over the high-rise buildings and industrial shapes looming around the shore at the park last week.

“This park has been here for around 30 years, and the people who use the park and the people involved in conservation in the park have been working together to preserve the mud flats,” he said. “So it’s fantastic that their work has been recognized. It’s a great source of pride for the people of Tokyo.”

Kasai Kaihin Park, a brackish wetland in Tokyo Bay located in the city’s Edogawa Ward, became Tokyo’s first-ever Ramsar Site and Japan’s 52nd when it was recognized by the Ramsar Convention last month along with Shizugawa Bay in Miyagi Prefecture.

The Ramsar Convention is an international environmental treaty established in 1971 focused on the conservation of wetlands. The Ramsar List is the world’s largest network of protected areas, with over 2,200 sites covering an area of over 2.1 million square kilometers.

Kasai Kaihin Park is a public park featuring two man-made beaches covering an area of approximately 412 hectares, and first opened in June 1989. One of the beaches is open for visitors to have barbecues, swim in the water and dig for clams, while the other is not connected to land and serves as a nature reserve closed off to the public.

“These mud flats are natural, but a lot of industries and homes sprung up around here with the economic development of the 1960s and 1970s, and there was also damage from typhoons,” Sakashita said. “So the Tokyo government decided to make this artificial beach to protect the mud flats.

“Because of that, the mud flats are still here and are home to a lot of wildlife and migratory birds. People have also harvested seaweed and caught fish on these flats for many years, and this park has allowed that way of life to survive and continue. So it’s a worthy place to be designated as a Ramsar Site.”

The Sanmaisu mud flats, formed where the mouths of the Arakawa and Kyu-Edogawa rivers flow into Tokyo Bay, provide the ideal living environment for organisms such as bivalves, crustaceans and bristle worms. They also act as a landing ground for migratory birds, including a variety of ducks.

A wetland must meet at least one of the Ramsar Convention’s nine criteria to become eligible for designation, and Kasai Kaihin Park fulfills three. Namely, it regularly supports 20,000 or more water birds; regularly supports 1 percent of the individuals in a population of one species or subspecies of water bird; and supports either or both plants and animal species at a critical stage in their life cycles, or provides refuge during adverse conditions.

About 10 percent of the global population of greater scaups — a midsize diving duck often known as a bluebill in North America — migrate to Kasai Kaihin Park for the winter. They are joined by about 3 to 5 percent of the population of great crested grebes — about 1,000 to 3,000 birds — and over the course of a year the park sees over 120 bird species.

“Usually you can see lots of greater scaups and great crested grebes about now, but we haven’t seen any today,” said Kunio Osawa, a birdwatcher from the Tokyo suburb of Fuchu, as he made his way across the sand toward the closed-off east beach with three companions. “I think this year the birds are a little later than usual. We’re going to have a look at the east beach through the long lens.”

The park also acts as a breeding ground for little terns, which arrive in the summer after spending the winter months farther south. Around six or seven years ago it was discovered that the birds were laying their eggs on the public west beach, so park officials created a special area for them to breed in and invited visitors and local residents to make decoy birds to attract them to it.

With about 600,000 people visiting Kasai Kaihin Park each year, the coexistence of people and nature is a delicate balance. The park is a popular spot for picnics and barbecues, and is connected by bridge to the larger Kasai Rinkai Park, which houses the Tokyo Sea Life Park aquarium.

Visitors can also splash around in the sea off the west beach in the summer, and with so few places to take a dip in natural surroundings in the Tokyo area, park officials have no intention of spoiling people’s fun.

“If you want to preserve an area in pristine condition, you have to restrict people coming into it,” said Sakashita. “But Tokyo people have been using these wetlands for fishing and recreation for many years and it has become a part of their lives. It’s necessary to preserve that as well.

“On the other hand, we want to preserve the natural environment, so we have the east beach where no one is allowed to go, and fish, shellfish, crabs and waterbirds can live undisturbed. We have to think about the balance between people’s lives and preserving the environment.”

Another challenge that park officials have to contend with is Tokyo Bay’s notorious water quality. The issue has returned to the spotlight recently as organizers of the 2020 Games prepare to hold parts of the triathlon and marathon swimming events at Odaiba Marine Park, and Sakashita admits that the struggle is constant.

“The population is becoming more concentrated in the city, so if you compare it with the Ogasawara Islands or Okinawa, for sure there is a problem with the water quality,” he said. “But if you compare it now with how it was here 40 or 50 years ago, it has improved a lot.

“Whether that continues depends on the efforts that go into it. One of the things that Ramsar praised was the balance that has been preserved given the impact of the people using the park. But we want to keep trying to make it better.”

The Tokyo Metropolitan Government will hold a public event to commemorate the Ramsar Site registration at the park on Saturday, with Tokyo Gov. Yuriko Koike set to speak and visitors invited to observe the coastal wildlife and take part in a voluntary beach cleanup.

Searching for shells on the west beach with her 2-year-old son, Koki, local resident Saori Hattori was pleased to learn that the park had been given special status.

“I’m surprised that somewhere that’s close to where we live and is part of the city like this has been chosen as a registered place,” she said. “We come here often when the weather is good. There’s lots of nature and wide-open spaces, and my son likes to run so it’s perfect. You get the sea and the woods and I like that.”

Sakashita will be at Saturday’s ceremony and he is happy that the work that has gone into preserving the mud flats is receiving recognition. With Kasai Kaihin Park enjoying its moment in the spotlight, he is also hoping that more people will play an active role in its upkeep.

“I think this park being recognized by Ramsar is very important,” he said. “It gives you a sense of responsibility to preserve it. Of course the Tokyo Metropolitan Government has a responsibility for that, but this is a great opportunity for all people to get involved in conservation efforts along with us.”