The lagoon, which is situated at the foot of Quan Cau Pass near National Highway 1A in Tuy An District, is the shape of a swan when viewed from a plane passing overhead. The 1,200ha wide lagoon with an average depth of 1.2m to 1.4m is surrounded by rolling hills, and linked to the Cai River. A small creek also links the lagoon and the sea.

Golden sand dunes and casuarina forests also line the banks of the lagoon, providing shelter for pelicans, storks and ducks.

According to traveller Nguyen Manh Dung, one of the most enjoyable things to do at O Loan is to jump into a boat to cruise the lagoon. Local boatmen will take you out across the calm waters, "and you may even be surprised to see fish jumping out of the water," said Dung. "One even jumped into my boat."

O Loan lagoon is famous for culinary specialities such as red oysters, cuttle-fish, jelly fish and a type of red algae that is used in food.

"The seafood here, especially the red clams, are very delicious because of the scent and sweet taste," said Dung.

There's a famous saying here: "One can not say that they have visited Phu Yen without having tasted O Loan's blood cockles."

These saltwater clams are thought to be extremely healthy to eat. They're also extremely yummy, and called "blood cockles" because the meat of the clam looks red.

They contain the highest nutritional content when compared to other clam or oyster species in Viet Nam.

The clams can be grilled, boiled or steamed but grilling is the most simple and delicious way to prepare them. Dinners can enjoy a wide range of clam dishes such as clams with rice porridge, stir-fried clams and more, and which ever dish you choose, it's best to eat it while out on the water.

Diners can enjoy the dish with a dipping sauce of salt, pepper and lime juice, spicy vegetables, grilled girdle cake and wine.

Le Hoang Sang, chairman of district's People's Committee, said O Loan is one of Tuy An District's most important tourism destinations.

"The value of O Loan is in both its beautiful landscape and unique specialities which are the means of subsistence for locals here," said Sang.

According to him, the environment in the area is very clean, an important factor that has helped to preserve the natural beauty here. In 1996, the lagoon was recognised by the Ministry of Culture, Sports and Tourism as a beauty spot that must be protected.

Many enterprises have asked to breed other types of seafood in the lagoon but have not been allowed to do so by district authorities keen on preserving the ecosystem.

If you want to discover other landmarks in the district, you'll have to get back onshore. Near O Loan Lagoon to the north is Mang Lang Church in An Thach Commune, one of the oldest churches in the country that is home to one of the first books printed in Vietnamese romanised script.

Not far from the church is the historical Quang Duc pottery village, which was settled in the 17th century and saw a period of strong development during the 18th century. The outstanding feature of Quang Duc pottery is the enamel covering on the pottery, which incorporates clam shells form O Loan lagoon.

The picturesque Da Dia Reef is located in the area in An Ninh Dong Commune. It is 50m wide and stretches for more than 200m. It is made up of thousands of pentagonal rocks, causing passers-by to stop and contemplate the unusual and magnificent landscape.

Next to Da Dia Reef, there is a sand beach that stretches for about 3km. The sand here is white, clean and smooth, the water is clear and blue, making it a still unspoilt seaside haven for tourists. The scenery here still keeps its isolated beauty and the pristine environment.

Travellers who want to visit the area when it's at its most liveliest should plan their trip during the O Loan Lagoon Festival, held on January 7th on the lunar calendar every year. You'll get the chance to see traditional boat racing and a range of Phu Yen's traditional folklore features. The festival attracts thousands of people on the occasion of the Lunar New Year.