1.First, take pieces of a dirt in one direction. Create another right next to this in a parallel fashion. Repeat until you have what looks like a sandy beach.
2.Place some coconut trees, palm trees, and banana trees on this new sand
3.Plow some land next to the dirt paths, once you are done making your sand. This image shows a similar technique with a hill added in.
Below is an example of the finished product.
Here some Video How to make ocean or lake with a beach.