Multiple planes with a water shader that exposes normal map and tiling parameters to create effects like current direction, water foam and intensity.
Reflective water is what is being used here, as it is made to reflect whatever is on top of it. This is better for oceans as you cannot see the seabed (if there is one) and it reflects the light from the sun and skybox.
Refractive water is better for streams and murky waters, as it will reflect anything that is below it. This means if you have a rocky seabed, the water will reflect and it will become crystal clear water that you can see through with ripples and slight distortion.