The phrase "choppy seas" means that the water in a particular area or body of water is rough and uneven, with waves rising and falling unpredictably. Full definition
The extent to which Matisse was disturbed by the angularity and the relief - like choppy sea of planes in the Demoiselles is revealed in the Bathers with a Turtle. (abcrit.org)
We're still bouncing around on choppy seas and should be through the end of the year. (activerain.com)
The most powerful waves create the most mixing, so the images could be used to warn mariners away from choppy seas. (discovermagazine.com)