Largely because of its shallowness, the surface water temperature of the Yellow Sea is lower than that of the East Sea in winter and is higher in summer. The East Sea averages approximately 5℃ in winter near Gangneung and 23℃ in summer near Hamheung. An abrupt discontinuity in temperature exists near theseareas, however, because of the influence of the Tsushima Warm Current and North Korea Cold Current. The portion of the Yellow Sea and East Sea belonging to North Korea's territorial waters shows a remarkable annual temperature range of approximately 20℃. Ranges are not as large in the East Sea adjacent to Gyeongsangbuk-do, and along the south coast.

Surface water temperature adjacent to Boryeong in Chungcheongnam-do fluctuates most remarkably. Water temperature around Jeju remains between 18 to 27℃ throughout the year because of the influence of the warm Kuroshio Current; subtropical biota can be found around the island because of the consistently warm water year-round. Near the Straits of Korea, water temperature remains at 12 to 15℃. However, water temperatures fall below 10℃ around the northwest part, which receives the effect of the Yellow Sea cold water. For this reason, a front develops between the two zones.

The surface of the South Sea generally remains between 25 and 29℃ in summer. Waters around the islands from Tongyeong to Yeosu are influenced little by waves, so that warm-water fish are cultivated using enclosing nets. However, the 'red tide' phenomenon can cause large-scale fishkills in this region. August is the most frequent month for red tide, which occurs when the surface water temperature exceeds 25℃. Under such conditions, the influx of domestic sewage and factory wastewater into the sea causes explosive expansion of the population of toxic plankton and the red tide, resulting in the depletion of oxygen or eutrophication of the water body. The red tide disappears after surface water temperature falls below 25℃, decimating the plankton.

Surface water temperature of the East Sea averages 26 to 27℃ in the east and 18 to 20℃ in the north during summer. In winter, averages are 13 to 14℃ in the south, but less than 4℃ in the north. The annual range of water temperature is over 20℃ in the north and about 13℃ in the south. At a depth of 10 m, the southern East Sea in summer is at about 15 to 17℃ and the northern part is 2℃. A front develops around Jukbyeon and the waters near Ulleungdo, separating waters influenced by warm and cold currents. In winter, temperatures average from 13 to 14℃ in the south and 5 to 6℃ in the north. During the winter, the Yellow Sea is between 2 and 8℃ because of the influence of a continental climate and the shallow waters of the Yellow Sea. In the summer, it warms to 24 to 28℃, for an annual range of 20 to 22℃. At a depth of 50 m, water temperatures in winter are about the same as at the surface, but temperatures rise only to 15℃ in the warm season. A well-developed thermocline forms at depths between 10 and 30 m, with warm surface water flowing northward under the influence of a southwestern wind and colder bottom waters running southward.

Surface salinity of adjacent waters ranges from 27.0 to 34.5‰ on the average, but varies by area and season. The East Sea is more saline than the other water bodies, and the Yellow Sea is the least saline. In the South Sea, the water adjacent to the Kuroshio is more saline than other water. In winter, salinity increases because of the reduced freshwater input from dry mainland Asia. The summer rains reduce the salinity, despite increased evaporation.

Surface salinity in the South Sea begins to increase from autumn until it peaks in April at about 34.5‰. Afterwards, it decreases to below 33.0‰ in August. Values of about 34.5‰ occur around the Tsushima Warm Current in winter, and a salinity front forms between Jeju and the Yangtze River from which Chinese coastal water flows. Values of about 32.2‰ around the Straits of Korea occur in the summer, and a salinity front is distinct between the Kuroshio waters and the continental shelf around the East China Sea.

Salinity of the East Sea may reach 34.5‰ around the Straits of Korea in winter, and falls to 33.0‰ in summer because of lower-salinity water input from from the East China Sea and the Yellow Sea. Salinity decreases to 30.0‰ in some places. The annual range of salinity is about 1.5‰ around the area influenced by the Tsushima Warm Current, but it usually remains near 34.1‰ throughout the year under the area of the warm current.

Surface salinity of the Yellow Sea during the winter is about 31.4‰ and 33.2‰ in the north and south respectively. A salinity front forms between the warm current and the cold water of the Yellow Sea. In summer, it is less than 31.0‰ near the coast and between 31.2 and 31.8‰ around the middle, with a salinity front forming between the two areas.