Alvin - this is a very broad question - but this is what i would do:
find the middle blue color of the water.
Paint the entire area of water in that color.
get a tissue and spray it with white - then dab that tissue with white, over the sea area to create all of the textures underneath.
Then lightly spray over the whole area with white.. maybe 10% white.
then go in with the middle blue color once again and start to establish the shapes moving almost from left to right very lightly.
use a slightly darker blue for darker areas and highlight the white areas with straight white. hope this helps? i'm sure Alvin would love a hand if anyone else could help him out also?