uncharted water

uncharted water (countable and uncountable, plural uncharted waters)

1. An area of sea that has not been surveyed, or whose details have not been entered on nautical charts.
2. (figuratively, in the plural) Any unknown and potentially dangerous situation.

   Synonym: uncharted territory

   • 1900, Walter Hines Page, Arthur Wilson Page, The World's Work ...: A History of Our Time:

     That is the rock that he is in danger of, for he is going recklessly over uncharted waters.

   • 2016 February 2, Stephen Burgen, “Spain in uncharted waters as king asks socialist leader to form government”, in The Guardian‎:

     Spain has effectively been a two-party state since democracy was reinstated in 1978 and the current stalemate is unprecedented. For King Felipe, who has been on the throne for only 18 months, these are also uncharted waters.

   • 2019 September 25, Geoffrey Kabaservice, “Impeach Trump? The United States is now in uncharted waters”, in The Guardian‎:

     As a country, we now enter what the seven freshmen called “unchartered waters”, with an unprecedented political and constitutional crisis looming on the horizon.