open water

(uncountable, usually) An expanse of an ocean, sea, or large lake which is distant from shore and devoid of nearby islands or other obstructions.
(uncountable, usually) In a river, pond, or other small body of water, an area of surface unobstructed by aquatic vegetation, boulders, and the like, adequate for navigation or swimming.
(Canada, uncountable, usually) An area of an ocean, sea, lake, or river which is not covered by ice.