Purple loosestrife

It was a clear sunny day. Lots of leaves still clung to the trees and there was a slight breeze. We selected our spot and placed our quadrant near the water's edge. We noticed plants with red leaves and tiny thorns; we also saw leaves looking like lilies or reeds? We saw lots of ragweed. We saw another plant with lance-shaped leaves that we almost thought was the species we were looking for. Upon closer observation...it was not. There were three granite slabs separating the area we examined from the area farther from the water. We were wondering if these were used for erosion control. We heard birds in the distance, a woody aroma and ripples in the water. We were surprised to find as many species as we did in the small area, and wondered if we would find the elusive Purple Loosestirve.