When you reach the edge of Kenilworth Aquatic Gardens, there is a long boardwalk that leads you to the Anacostia River. It's a lovely view with very little to indicate you are within a major city. The semi-wet soil in which the pink perennial below is growing is a typical habitat for Vernonia noveboracensis or New York Ironweed.
New York ironweed is a native to the northeast and though it's regularly found on the edges of streams, it can also fare well in drought or heavy soils. It can easily reach heights of 6-8' and works great with other late summer flowers like sunflowers and goldenrod.
Finally, the deep magenta blossoms (like all flowers in the Asteraceae family, the flowers are composites with disc and ray florets), add a powerful pop to an otherwise dull late summer garden.
