The phrase "high seas" refers to the vast oceans that are not owned or controlled by any specific country. It means the parts of the ocean that are far away from the shore and are not under the jurisdiction of any nation. Full definition
The national and international dimensions of and efforts to curb human - caused climate change are in stark contrast to the very local, and disproportionate, potential impacts of higher sea levels. (treehugger.com)
This year the area of high sea levels is less intense but considerably broader. (psmag.com)
Then again, I've always been a sucker for high seas adventures. (toy-tma.com)