What “water quality” covers
Water quality is not one measure. It describes a set of conditions that scientists and regulators track, such as dissolved oxygen, bacteria levels, nutrients, temperature, clarity and the presence of chemical contaminants. A river can score well on some and poorly on others, and the right measure depends on the question being asked: whether fish can survive, whether people can swim, whether the water can be treated for drinking, or whether sediments are safe to disturb.
This article gives a general account of how rivers recover from pollution, using the Delaware as the setting. It does not report current readings, which change and are published by environmental agencies.
Where the pollution came from
Rivers near large cities have historically received waste from several kinds of sources:
- Sewage. Untreated or lightly treated household and commercial waste used to flow directly into many rivers.
- Industrial discharge. Factories, refineries and processing plants released wastewater and, in some eras, hazardous materials.
- Stormwater and runoff. Rain washing across streets, rooftops and lawns carries oil, trash, fertilizer and bacteria into storm drains and streams.
- Combined sewers. In older cities, one set of pipes carries both sewage and stormwater. In heavy rain, the system can overflow and release a mix of both into the river.
The lower Delaware was affected by all of these during its long industrial period. In the mid-twentieth century, stretches of the tidal river near the cities had very low oxygen in warm months, which discouraged fish from migrating through them. Readers interested in the industrial context can look at the article on industrial Camden.
How a river can recover
Rivers are not static, and they can recover when pressure on them is reduced. The usual path involves several steps.
Stopping the source. The most important step is cutting what enters the water. After the passage of national clean water legislation in the 1970s, requirements for wastewater treatment and permits for discharges became stricter. Upgrades to treatment plants typically reduced organic waste, which in turn allowed oxygen levels to rise.
Natural processes. Flowing water dilutes pollution and carries it downstream, and bacteria and other organisms break down many organic materials. The tide in an estuary adds mixing but can also move contaminants back and forth.
Habitat and biology. As oxygen improves, fish and invertebrates return, and birds that depend on them follow. Wildlife is often used as an indicator, though not a perfect one, a point also noted in the article on the fish, birds and wildlife of the Delaware’s tidal waters.
Cleanup of legacy contamination. Some pollutants settle into river-bottom sediment and persist for decades. Dealing with them can involve study, removal, capping or monitoring, and the process is slow and costly. The land side of this problem is described in the article on brownfield redevelopment and in the discussion of industrial contamination.
What recovery does not mean
Improvement is not the same as a finished job. Several caveats apply.
- Recovery is gradual and uneven. Some measures improve sooner than others, and conditions vary by location and season.
- Legacy chemicals may linger. Certain contaminants break down very slowly, so advisories about eating fish from urban waterways may remain even when the river looks and smells better.
- New pressures appear. Population growth, development, nutrient inputs and changes in climate and rainfall can create new challenges.
- Swimming and recreation depend on conditions. Bacteria levels can rise after heavy rain. Anyone considering contact with the water should follow current notices from health and environmental agencies.
Stormwater and the city
Because rain is a main modern source of pollution, cities increasingly look at ways to slow and absorb it before it reaches the river. Tools include rain gardens, permeable surfaces, street trees and upgraded sewer systems, which are described under green infrastructure. These approaches also help reduce flooding in low areas, a theme in the discussion of the tidal floodplain.
How residents can follow progress
Information on water quality is published by federal, state and regional agencies and by watershed organizations. Reading any one report carefully, with attention to the date, location and what was measured, is better than relying on a single headline. Fish consumption advisories, beach and swimming notices and sewer overflow reports are specific kinds of information with their own sources.
A realistic picture
The Delaware’s story is often told as a recovery, and it is fair to say conditions have improved in significant ways since the mid-twentieth century. It is also fair to say that the river remains an urban, industrial waterway with continuing challenges. Holding both ideas at once is the most accurate way to describe it.