Low levels of dissolved oxygen in the canal's waters predate World War I. The minimum level of oxygen required to support healthy marine life is estimated at 4 parts per million. As early as 1909, it was reported that the canal had no oxygen at all. In 1975 a severe lack of oxygen was still observed, indicating the water was incapable of sustaining plant life or fish. In 1999, just before the flushing tunnel was reactivated, "The Environmental Magazine" reported that oxygen levels in the Gowanus Canal measured about 1.5 parts per million; this number continued to be quoted fourteen years later. However, by 2008, nine years after the flushing tunnel was reopened to provide oxygenation of the water, biologist Kathleen Nolan and students from St. Francis College sampled the water and reported that levels of dissolved oxygen had substantially increased. In 2014, a NYSDEC representative stated that dissolved oxygen levels were reported to be in the range of , or approximately 9–12 parts per million.