Except for a dozen or so mountains, including Manisan Mountain (469m), Gyeyangsan Mountain (395m), and Samgaksan Mountain (343m), most of Incheon sits below 300m above sea level. As such, there are no major rivers originating from Incheon and its surrounding areas. Some smaller rivers such as Gulpocheon, Cheongcheoncheon, and Gyesancheon flow into Hangang River, while others such as Sicheoncheon and Gongconcheon to the north and Seunggicheon, Mansucheon, Jangsucheon, and Unyeoncheon to the south drain into the Yellow Sea. All rivers, except Gulpocheon (11.5km), are less than 10km in total length - e.g. Seunggicheon (6.2km), Geomdancheon (6.74km). Incheon has a rias coastline, which means it has a long and complicated shoreline with plenty of islands. More specifically, Incheon has 168 islands in total, 128 of which are deserted islands with no inhabitants.