http://www.sciencemag.org/news/2020/08/secret-hidden-centuries-old-mud-revealed-new-way-save-polluted-rivers

As the result of a restoration project that removed 22,000 tons of colonial-era sediment, Big Spring Run in Pennsylvania now snakes through lush wetlands.

BIG SPRING RUN IN PENNSYLVANIA—Centuries ago, parts of the eastern United States were drowned in mud. Now, Robert Walter was dancing in it. The geochemist stood calf deep in this small stream 100 kilometers west of Philadelphia, thick curlicues of chocolate sediment flowing around his legs. Walter did a little jig as his colleague and spouse, geomorphologist Dorothy Merritts, watched. More mud stirred, heading downstream.