Healthy lands and underwater grasses provide critical habitat for animals, and play a critical role in keeping our waters safe and clean.
Underwater and shoreline grasses provide shelter to many species, add oxygen to the water, and reduce streambank erosion. Forests and trees along rivers absorb nutrients, capture sediment in runoff, and stabilize riverbanks.
Though overall pollution levels have decreased in recent years, underwater grasses and water clarity have been slow to recover. While dissolved oxygen levels are going up — a mark of a healthier river — amounts of chlorophyll a and water clarity are going down. Tidal grasses are faring better in recent years, but are far from meeting restoration goals set by the Environmental Protection Agency.
Previous Grade: C-
Data on dissolved oxygen, water clarity, and chlorophyll a (a measure of algae) offer a snapshot of tidal water quality in the Potomac River. Improved dissolved oxygen and water clarity in the Potomac can produce ideal conditions and habitat for fish and other aquatic life.
While dissolved oxygen levels have been relatively high in recent years, the river continues to suffer from poor water clarity. Overall tidal water quality conditions remain unchanged over the last several years.
Harmful levels of pollution impair water quality, but storms and other extreme weather events can cause disastrous river conditions as well. For instance, flooding events in 2003 and 2011 contributed atypically high levels of sediment to the Potomac’s waters which led to degrading water quality conditions in those years, as evident in the chart.
Taken together, the combined average of dissolved oxygen, water clarity, and chlorophyll a meet 40.1 percent of target goals. The last river report in 2013 graded tidal water quality at a C-.The University of Maryland has created a flow-adjusted measure of water quality for the Chesapeake, but this does not yet exist for the Potomac.
Previous Grade: D
Underwater grasses provide habitat for fish, waterfowl, and other wildlife, and they require clean water. Restoring healthy tidal grass beds to the tidal Potomac goes hand-in-hand with other water quality improvements. Several restoration programs have aimed to bring grasses back to the Potomac.
Pollution and sediment can alter and destroy subaquatic vegetation. Local fishermen report that tidal grasses near the Woodrow Wilson Bridge were destroyed and have not recovered as a result of construction to the bridge and National Harbor.
A University of Maryland analysis found that tidal grasses in the Potomac rebounded in the past two years, but continue to fall far short of the restoration target. Tidal grasses are meeting 41 percent of the threshold goal up from just 32 percent in 2012. The last river report in 2013 graded underwater tidal grass at a D.
Previous Grade: C-
Shoreline trees (forested buffers) offer crucial protection from harmful effects of pollution, sediment, and water temperature fluctuations in local streams and creeks. Forests in rural Maryland, Virginia, and West Virginia provide the cleanest waters to the Potomac River.
According to the US Department of Agriculture Conservation Reserve Program, around 15,170 acres of agricultural forest buffers have been planted in the Potomac Basin as of 2012, roughly 40 percent of the acres needed to reach the Potomac River’s 2025 Watershed Improvement Plan (WIP) goals.
Data on forested buffers in the Potomac region has not been updated since the 2013 report; updated analysis is expected to be released in 2016.
Previous Grade: D
Impaired water quality is a common challenge for our nation’s rivers and streams, and the Potomac River is no different. To assess the health of non-tidal streams and wadeable rivers, the Chesapeake Bay Benthic Monitoring Program developed a special health index in 2012 that combines data from a variety of monitoring programs. Based on this index provided by the Interstate Commission on the Potomac River Basin, the average, area-weighted score for Potomac River stream health is 35.91, or “Fair” (bordering on “Poor”).
It’s estimated that 52 percent of sub-watersheds sampled in the Potomac River are in excellent, good, or fair health. A watershed is deemed in good health if 70 percent of its streams and rivers are in excellent, good, or fair health.
Data on stream water quality in the Potomac region has not been updated since the 2013 report; updated analysis is expected to be released in 2016.