The Clean Water Act and Water Quality

This past Thursday marked the 40th anniversary of the Clean Water Act. We’re celebrating the act’s big 4-0 by highlighting the ways we use our local waterways and our shared responsibility for protecting those uses.  We’ll also be featuring some of the work we do, utilizing the Clean Water Act’s tools, to protect the quality of our local waterways.

First up: lets look at how the Clean Water Act protects and improves the quality of our local waterways. The Clean Water Act is revolutionary because it devised a two part system to attack water pollution.  The first part deals with pollution at the source where it is created and discharged. [Stay tuned for more on this]  The second part deals with the in-stream water quality of local waterways and is the subject of this post.

Water Quality Standards

The Ashley/Cooper River Basin a/k/a the Charleston Harbor Watershed

Water quality standards are the foundation for protection of in-stream water quality.  In South Carolina, DHEC is responsible for developing and maintaining our water quality standards.  Simply put, water quality standards are goals for the in-stream water quality of a waterway.  They have three parts: (1) a designated use, (2) water quality criteria, and (3) antidegradation rules.

A “designated use” is an officially recognized human or ecological use for a particular waterway.  For example, DHEC classifies recreation as a designated use of Shem Creek.  Other designated uses include protection and propagation of fish and shellfish, public water supply, and agricultural and industrial uses.  A single section of a waterway may have more than one designated use, and different sections may have different uses.  Every waterway must have at least one designated use.

All designated uses must be protected.  DHEC accomplishes this by defining the “water quality criteria,” or the level of water quality, necessary to protect each designated use.  Water quality criteria are set using data and scientific judgment about the impact of water pollution on each designated use.  They can be numeric limits on the amount of a pollutant or a narrative description of the desired water quality.

Existing water quality must be maintained.  The primary tools for maintaining water quality are “antidegradation rules.” These rules are designed to minimize the impact of new or expanding sources of pollution on in-stream water quality.  Properly developed and implemented antidegradation rules can protect existing water quality from deterioration.

Impaired Waterways

Water quality standards are essential for protecting our right to clean water.  But merely setting goals for water quality is not enough.  That’s why the Clean Water Act requires each state to develop a list of waterways that do not meet water quality standards.

This list, known as the 303(d) list, requires states to review existing water quality data and determine which waterways do not support their designated uses.  These waterways are known as “impaired waterways.”  Each state develops a 303(d) list every 2 years.  In South Carolina, DHEC develops our 303(d) list.  According to the last 303(d) list, approximately 41% of waterways statewide are listed as impaired.

The most recent data available for our area indicates there are 102 impaired waterways in the Ashley/Cooper River Basin.  That means the quality of the water in 102 of our local waterways makes them unfit for their designated use. The impacted uses in our area are highlighted in the pie chart below.

These 4 designated uses are impacted by a number of different “impairments” or pollutants.  The high levels (or low levels in the case of dissolved oxygen) of these pollutants make waterways unfit for their designated uses. A single waterway can have more than one impairment impacting more than one designated use.  The impairments for our area are reflected in the bar graph below.
More than half of the impaired waterways in our area are impaired for fecal coliform. Fecal coliform is an “indicator bacteria” which points to the possible presence of fecal pollution.  Fecal pollution is exactly what it sounds like and comes from many different sources.  It impacts recreational and shellfishing uses of our waterways.  Fortunately, DHEC regularly monitors local shellfish beds for potential contamination and warns the pubic and shellfish harvesters.

Twenty-one percent of the impaired waterways are impaired for low dissolved oxygen. Dissolved oxygen is simply oxygen dissolved in water.  Just as we need air to breath, fish and other aquatic life need dissolved oxygen for respiration.  A wide variety of pollutants lower dissolved oxygen levels when they are discharged to our waterways.

Ten percent of the impaired waterways are impaired for high levels of mercury. One source of mercury is coal burning power plants.  As coal is burned mercury is released to the air.  When it rains, mercury returns to the ground with rainfall where it enters our waterways and contaminates fish and other aquatic life.  Mercury is highly toxic and DHEC warns about eating several species of fish caught in our local waterways that are contaminated with mercury.

Explore the impaired waterways in your area using this map:

View Ashley/Cooper River Basin Impaired Waterways in a larger map

Total Maximum Daily Load (TMDL)

After determining which waterways do not meet their water quality standards, the next step is to develop a plan for fixing the cause of the impairment.
A “Total Maximum Daily Load,” or TMDL for short, is a two part plan to improve the quality of an impaired waterway. The first part is a cap on the maximum amount of a pollutant a waterway can receive and still meet its water quality standards.  The second part is a plan that describes how each source of a pollutant must be reduced.  After an impaired waterway is identified, DHEC is responsible for developing TMDLs.

In our watershed several waterways have TMDLs in place for fecal coliform or low levels of dissolved oxygen.  These are highlighted in the interactive map below.

View Ashley/ Cooper River Basin TMDLs in a larger map

TMDLs can be and have been successful in helping some of our impaired local waterways meet their water quality standards.  Unfortunately, TMDL development is slow and DHECs resources for developing and implementing TMDL have dwindled.

Wrapping It All Up

The Clean Water Act uses a three part approach to protect the quality of our waterways: goals, evaluation, and intervention (water quality standards, 303(d) list, TMDLs).  Underlying this framework is the notion that local water users have the best knowledge of their local waterways and therefore the highest interest in protecting them.  That’s why the Clean Water Act provides for public participation at every stage, from establishing and updating water quality standards to TMDL development.  Charleston Waterkeeper uses these tools to identify water pollution hotspots and advocate for our right to swimmable, drinkable, fishable water.  You can participate by supporting this work with a $40 donation.  Join us.  Become one of the 400.  GIVE 444.


Fly Fishing in the Ashley/Cooper River Basin


You are donating to : Charleston Waterkeeper

How much would you like to donate?
$10 $20 $30
Would you like to make regular donations? I would like to make donation(s)
How many times would you like this to recur? (including this payment) *
Name *
Last Name *
Email *
Additional Note