Since the mid-19th century, the natural topography of New York City has been altered, sometimes by the filling in of adjacent waterways to create more land and sometimes by the excavation of land to create new or larger waterways. Both activities occurred in and around the Canal.
In the 1840’s, the Gowanus Creek was a tidal estuary flowing into the Gowanus Bay, in New York Harbor. At that time the creek was surrounded mostly by farms and mills.
As the City of Brooklyn began to grow and compete with the City of New York, elected officials decided to convert the creek into a canal to serve as a transportation system to help promote commerce and industry, much like the Erie Canal had done earlier.
The construction of the Canal began in 1849 and was accomplished by deepening and widening the Gowanus Creek and creating bulkheads along the waterfront. The Canal was fully built out by 1869.
Even before it was complete, the Canal was attracting foundries, shipyards, gas manufacturing plants, coal yards and paint and ink factories to the waterfront and adjacent lots. By 1870, the surrounding area, with its natural marshlands and freshwater streams, had been fully urbanized and industrialized.
Notably, there was little environmental regulation at the time and, as was typical for the 19th century and most of the early 20th century, waste from these industries was discharged directly to adjacent waterbodies without treatment. As a result, the Gowanus Canal became contaminated with a host of industrial pollutants, such as coal tar and heavy metals (e.g. mercury, lead).
There were three manufactured gas plants (MGPs) located along the Gowanus Canal, which are believed to be sources of much of the polycyclic aromatic hydrocarbon (PAH) contamination in the Canal—the former Fulton MGP site; Former Citizens Gas Works MGP site (a.k.a. Carroll Gardens/Public Place); and former Metropolitan Gas Light Company MGP site (MGP Sites). At the MGPs, coal was converted to gas, which was used for lighting, heating and cooking. National Grid is conducting cleanups of the MGP Sites under the oversight of the New York State Department of Environmental Conservation (DEC). These sites exhibit the characteristics and contaminants expected of former MGP sites, including the presence of coal tar and dense non-aqueous phase liquid (DNAPL).
In the early 20th century, city planners and engineers decided that something had to be done to improve water quality in the Canal. Since the Canal did not have a natural flushing action, City engineers decided to build a tunnel to flush the Canal by drawing water from the head of the Canal near Butler Street, conveying it through a 1.15-mile tunnel, and discharging it into Buttermilk Channel. The Flushing Tunnel was completed in 1911.