Japan Current
Kuroshio Current
proper noun
The black tide isn't what you think, most likely. This is the Japan current, aka the Kuroshio Current. It's a Northern flowing current on the West side of the Pacific Ocean. Have you heard of the Gulf Stream? It's kind of like that.
The reading is the kun'yomi readings of the two kanji, put together. 黒 and 潮.
黒潮の流域とは正確にはどこになりますか？
Where exactly is the basin of the Kuroshio Current?