How to extract a coastline of the lake for fractal analysis

I am new to ImageJ software. I want to extract the boundary of the lake which I am analyzing. I am outlining the method that I saw in a article. The author says:

" As an example we take the Noanamakki Reservoir whose image is shown in Fig. 1. We first extract the boundary of the lake one is analyzing. In order to achieve this, the water body is first colored black and then the binary image consisting only the water body is extracted (Fig. 2).Then the edge detection algorithm is used to obtain the boundary of the lake as depicted in Fig. 3"

I wonder how I achieve the above method using ImageJ.

• Fig1:

• Fig2:

• Fig3:

It may help to apply the magic wand tool to an image that results from a colour space transformation. I tried it with the 8bit b*-channel after Lab-transformation. Setting the wand tool to Legacy, and using a tolerance of about 30 works quite well. However, some lake regions may need retouching. Here are the binary images of "Lake Powell" (with the "Glen Canyon"-dam at the bottom) that correspond to the images you've shown: The original image is from the link posted in my comment.