潟湖 is read as せきこ (sekiko) and means lagoon.
せきこ
sekiko
かた
lagoon
ふじごこ
the Five Lakes of Mt. Fuji
ふえいようこ
nutrient-rich (or eutrophic) lake
みずうみ
lake
びわこ
Lake Biwa
みかづきこ
oxbow lake
ちかこ
underground lake
じんこうこ
artificial lake
かこうげんこ
crater lake
しぜんこ
natural lake
じんぞうこ
ゆうこうこ
exorheic lake