There was no through-flow of water and the canal was open at only one end, in the hope that the tides would be enough to flush the waterway. But with the canal's wooden and concrete embankments, the strong tides of fresh diurnal doses of oxygenated water from New York Harbor were barred from flowing into the channel. With the high level of development in the Gowanus watershed area, excessive nitrates and pathogens are constantly flowing into the canal, further depleting the oxygen and creating breeding grounds for the pathogens responsible for the canal's odor. Water quality measures of the concentration of oxygen in the canal were just 1.5 ppm, well below the minimum 4 ppm needed to sustain life. The canal water took on a reddish-purple color, and a colloidal mixture described as "black mayonnaise" accumulated on its bottom.