Nearly one million years ago, the site of the lagoon was a bay formed by tectonic movement. Later, the entrance to the bay was blocked up by sediment bed layers to form a lagoon. There is a beach strip between the sea and the lagoon.

The area of the lagoon is 4.84 square kilometers and the depth of the water is five meters. The annual mean temperature of its surrounding area is 11.5 degrees Celsius and the annual precipitation is 1 239 millimeters.

Living in the lagoon are flatfish, herring, dace, snakehead, carp, etc.

The southeastern part of the lagoon is linked by a narrow waterway with Lagoon Chonapho. The area is a habitat for endangered bird species including Aythya baeri (CR) and many other water-birds.

Sweet briers blooming red on the sandy beach, islets in the lagoon and thick woods around it add scenic beauty to Lagoon Tongjong.

And its mud has been used for the treatment of diseases from long ago.

Today, the lagoon has turned into a cultural recreation ground thanks to the wise leadership of the Workers' Party of Korea.