Gary drew me this quick sketch to illustrate how the lake should be shaped.
For the lake, I decided to work with NURBS, as opposed to polygons, because I could quickly model a very organic and curved shape. To do this, I went to the 'Curves' tab and selected the EP Curve tool, which allowed me to draw curves, simply by clicking. I created the shape in the Top view.
I then went to the Surfaces tab and selected 'Planar' to create the flat NURBS surface. I deleted the history of the surface and the original curve.
Next, I opened the Maya file which contained the polygon plane and ocean shader that I had completed a while back.
I opened Hypershade, selected the ocean shader and simply exported it to its own Maya file.
I reopened my NURBS surface and imported the ocean shader. In Hypershade, I assigned the Ocean shader to the NURBS surface.
After a batch render, here is the outcome.