2D moving sea

Is there anyway to give a top down 2D sea a bit of life?
im just using a flat texture, its boring. looks pretty, but pretty boring. Would be nice to make the sea a bit dynamic even if just a top down 2D sea. Whats the best technique to accomplish this? the image is very big. Like 30000x30000 lol, and i know this prob isnt the best way to handle big image backgrounds for big “maps”

Any ideas, anybody?