A lagoon located in Thongchon County, Kangwon Province, the lake is 2.94 km² in area, 11.8 km in circumference, 3.5 km long and 0.8 km wide on average.
It was originally an inlet on the east coast, the mouth of which was blocked by sand to form the lake, due to the upthrust of the ground and the wave motion of the sea over a long period.
It was named from a pavilion called Sijung on the shore of the lake.
On the bottom of the lake is a 4 – 5m thick layer of mud but it is sandy near the sea.
In the east there is a 300m-wide sandy beach, white-tinted, which forms a divide between the sea and the lake.
The average temperature of the area is 11.8°C annually, -1.1°C in January and 24°C in August, and the annual average precipitation is 1252mm.
The lake is connected to the sea by a small waterway.
For its therapeutic properties the mud is efficacious for the treatment of such illnesses as inflammatory diseases and nervous system disorders.
The lake abounds in fish species including carp, goldfish, silver carp and Aristichythys nobilis, as well as shrimp and shellfish. The lake, limpid and serene, surrounded by densely wooded hillocks and sandy beaches pink-tinted all over with blooming sweet briers, presents a beautiful landscape. The scene is further set off by the pine groves on the sand bank and the surging seas beyond.