50 years of Delaware Estuary Dissolved Oxygen

The Delaware River Basin Commission’s Delaware Estuary water quality monitoring program, which was initiated in 1967, is one of the longest running monitoring programs in the world.  One advantage of such a long data set is that we can see the changes to water quality over time.

Since 1967, summer dissolved oxygen levels have steadily improved due to active water quality management and the addition of secondary treatment to waste water treatment plants.  More work remains, however.  A dissolved oxygen sag persists in the most urbanized portion of the estuary, and daytime surface spot measurements may not reveal pockets of lower dissolved oxygen water that could continue to impact aquatic life.