Elevated vs. Impaired – What Do These Lines on Our Graphs Mean?

When nutrient levels become elevated, they can stimulate excessive algae and plant growth (think: Schumaker Pond in mid-July). 

As that organic matter dies and decomposes, the process consumes oxygen in the water that fish, crabs and other aquatic life depend on. In severe cases, this can create stressful or even harmful conditions for aquatic organisms. 

When we describe nutrient concentrations in the Wicomico River Watershed as elevated, we are essentially saying that they are higher than desirable and may contribute to ecological stress. Elevated doesn’t mean that the river has suddenly become unhealthy or unusable; rather, it’s a warning sign, particularly when those conditions persist over time. 

Impaired Waterways: Impaired is a regulatory term, not simply a description of how polluted a river may appear to be. Under the Clean Water Act, states are required to identify waters that are not meeting established water-quality standards for their designated uses such as supporting aquatic life, recreation, or fishing.

So, when the Wicomico River is described as impaired, it does not mean that the entire river is polluted all the time, that every location is unhealthy, or that people cannot use the river. Rather, it means that available data indicate that one or more water-quality standards associated with a designated use are not being met. When a water body is designated as impaired, additional planning and management efforts are required to address the underlying problems. Parts of the Wicomico River have been listed as impaired since the early 1990s. Today, impairment designations in various parts of the river are for uses including shellfishing, aquatic life and wildlife, and fishing.  

What it Means for the Wicomico: The Wicomico River has a long history of nutrient pollution and water quality challenges. Those challenges are one reason that restoration and mitigation work throughout the watershed has been an important focus for the City of Salisbury, Wicomico County, and local organizations like WET. 

Wastewater and septic system improvements, agricultural practices, and stormwater management all play a role in reducing pollution at its source. And while that work takes time, we are beginning to see encouraging signs in our monitoring data. As described in the article above, we are seeing downward trends in nutrient loads, particularly total nitrogen.

This is good news. But it doesn’t mean we can stop paying attention. A river can be improving while still experiencing nutrient concentrations that are higher than we would like. Likewise, being below an impairment threshold does not necessarily mean that there is no ecological concern. Water quality exists on a continuum and aquatic ecosystems respond to the cumulative effects of many different factors. 

Why the Distinction Matters: The elevated nutrient line helps us identify conditions that warrant attention. The impairment threshold provides a regulatory benchmark for understanding whether established water quality standards are being met. Neither line by itself tells the entire story of the river’s health. They are two different tools for understanding the health of our watershed and both help us to answer the bigger question: are we moving in the right direction?