I bet they did do some dredging............but most of that island was already there..........



Although the shoreline of the Potomac River in the District of Columbia was likely to have been littered with shoals, sandbars, and marsh flats, no documentation of these was undertaken until 1834. At that time, the United States Army‍‍ '​‍s Corps of Topographical Engineers identified extensive tidal flats below Long Bridge (the predecessor structure to the 14th Street Bridge). These varied in size, but the largest was 100 acres (400,000 m²) in size at low tide. By 1881, these extended from about the Old Naval Observatory down to Buzzard Point. Near the modern intersection of 17th Street NW and Constitution Avenue NW, the city's sewer system discharged into an extensive tidal flat, known as Kidwell's Meadows. Exposed to the air about half the time, the sewage began decomposing, creating a powerful, rank smell.^[5]
The southern part of the Pennsylvania Avenue district was flooded many times in the last three decades of the 19th century. Major floods occurred in October 1870 (during which Chain Bridge was destroyed), February 1881, November 1887, and June 1889 (the same storm which caused the Johnstown Flood).^[6] Floodwaters were high enough that rowboats were used on the avenue, and horse-drawn streetcars saw water reach the bottom of the trams.^[6] After a disastrous flood in 1881, the United States Army Corps of Engineers dredged a deep channel in the Potomac and used the material to fill in the Potomac (creating the current banks of the river) and raise much of the land near the White House and along Pennsylvania Avenue NW by nearly 6 feet (1.8 m).^[7][8][9] Much of the dredged material was used to build up the existing tidal flats in the Potomac River as well as sandbars which had been created by silting around Long Bridge.^[10] Reclamation occurred in three phases: Section 1 (what is now 135-acre (550,000 m²) West Potomac Park), section 2 (what is now the 277-acre (1,120,000 m²) area around the Tidal Basin), and section 3 (what is now 327-acre (1,320,000 m²) East Potomac Park).^[11] Congress formally designated these areas "Potomac Park" on March 3, 1897.^[12]
To ensure that the island was not eroded by the river, poplars and willows were planted along edge of the island to stabilize the shoreline.^[13] Over the next two decades, most of East Potomac Park lay untouched, and dense thickets of trees and brush grew up on the island.^[14] Dredging of the Potomac River continued even after East Potomac Park was considered finished, and additional dredged material