Recently in travelling back to New England I discovered ditches in the lowlands/wetlands of the shoreline on Google Maps satellite view. They are clearly man-made, but even with all the agriculture and fishing in the area, I cannot figure out the purpose of these. I have discovered that they seem to be all over New England, but sometimes it's not a.
What is the purpose of the man-made lines that appear in all these satellite images?
An example image is below, but it is not very high resolution. Here are some links that show the phenomenon: