Thanks! I used multiple sine waves combined together to create the waves at the beginning. By defining different variables like wave_height, wave_length, and water_spd I could control the look of the waves. In my case the water consist of 80 water tiles stacked side by side, and I simply draw the tiles one by one, where their tile index decides the sine waves' starting point (think when current_time is 0, then only the tile index (var tile) decides the y value of that tile. This ensures not all tiles are at the same height)
(current_time is the number of milliseconds since the game opened, so I divide by 1000 to convert to seconds)
The first wave has -current_time, so it moves in the opposite direction. Then the secondary sine waves are multiplied by a float, to make those waves longer and less defined. The result is that the first sine wave is much more obvious, while the other sines just disrupt a bit to help to make the motion less constant and more natural.
The water tile is just a simple sprite, so I could change its texture quickly if I wanted :)
Then finally the boat uses the same sine waves to make it bob up and down with the water. I also wanted make the player affect the waves, but didn't have time to implement it. Hope this helps! If you have any more questions I would be glad to answer :D