What does "Wd" mean in green areas, Weeds?

Some green areas close to shore at the mouth of the Cathance R, Bowdoinham, Maine that opens into Merrymeeting Bay are weeds, even at high tide, but they don't show the Wd. The Wd green areas of concern are further away from the coast. It is unlikely these areas are weeds at high tide. What is your experience?