open water

Short definition from Wiktionary

Noun

1. 1
   An expanse of an ocean, sea, or large lake which is distant from shore and devoid of nearby islands or other obstructions.
2. 2
   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.
3. 3
   An area of an ocean, sea, lake, or river which is not covered by ice.