Surface Water Quality

​​Quality of Streams & Lakes​

​​​​​​​​​​​​​​​​​​​​​​​Information about the quality of local streams and lakes is organized as follows. Please scroll down for more information about these topics.


​​The Stream Use Support Index (SUSI) was developed to communicate vast amounts of surface water quality monitoring data that is collected from streams throughout the City of Charlotte and Mecklenburg County. The scores are updated quarterly and represent data collected 12 times a year from 24 monitoring sites.  The SUSI, or score, is constructed around five categories of surface water quality data that represent the most important pollutants and indicators of environmental health including each year. This index or score is constructed around five categories of surface water quality data that represent the most important pollutants and indicators of environmental health including:

  • Bacteriological

  • Metals

  • Nutrients

  • Physical

  • Biological

See the following SUSI interactive map​ ​to see the surface water quality score for of the watershed where you live or for any address you choose! Scores range from 0-100, with a score of 100 indicating the best water quality possible. ​

Additional information about streams and lakes designated as impaired by the State of N.C., or waterbodies that are on the 303(d) list, please see the “Impairments” section on our Watershed Planning page​. ​


You can visit our newstory mapfor an interactive look at the lakes in Mecklenburg County.  This map will show you data from all of our lakes, information on how, where, and why we monitor, and how you can enjoy the lake. 

​The Lake Use-Support Index (LUSI) was developed to communicate vast amounts of surface water quality monitoring data collected from Lake Norman (with Lake Davidson and Lake Cornelius), Mountain Island Lake, and Lake Wylie along the western border of Mecklenburg County. These scores are updated every other month and represent data collected six times a year from 28 monitoring sites. The LUSI is constructed around four categories of surface water quality data that represent the most important pollutants and indicators of environmental health including:

  • Bacteriological (fecal coliform and e. coli)

  • Metals (arsenic, barium, cadmium, chromium, copper, lead, manganese, nickel, selenium, zinc)

  • Nutrients (chlorophyll A, nitrogen, phosphorus, nitrates, nitrites)

  • Physical (temperature, pH, dissolved oxygen)

Scores range from 0-100, with a score of 100 indicating the best surface water quality possible.  The LUSI maps also include icons that also show where it is safe for swimming. 

    • Lake Norman:  
         See the LUSI map for Lake Norman 
            A fish consumption advisory is in effect

    • Mountain Island Lake:   
          See the LUSI map for Mountain Island Lake 
            Fish consumption advisories are in effect for more than one species

    • Lake Wylie:  
        See the LUSI map for Lake Wylie ​
            Fish consumption advisories are in effect for more than one species

See also the Lake Monitoring Report​ for in depth information about lake water quality compared to state standards.  Lake Monitoring reports are typically updated every year.

No Wake Zones for Lakes in Mecklenburg County 

A No Wake Zone is an area of a lake or river where vessels are required to travel at an idle speed or a slow speed so no appreciable wake is created. No Wake Zones are typically defined by floating buoys. Only the Marine Commissions and the NC Wildlife Resources Commission can approve a No Wake Zone.

The Lake Norman Marine Commission and the Lake Wylie Marine Commission handle requests for the establishment of No Wake Zones on these respective lakes.

There is no Marine Commission for Mountain Island Lake so theNC Wildlife Resources Commission must approve No Wake Zones for this lake.  The NC Wildlife Resources Commission has appointed Mecklenburg County to administer the application process.

Mecklenburg County’s process for establishing a No Wake Zone, starting with submittal of an application, can take between one and two years to complete. The process is summarized as follows:

  1. Interested person submits an application for a No Wake Zone on Mountain Island Lake.

  2. Mecklenburg County Board of County Commissioners (BOCC) advertises in a local newspaper the date, time and location of a public hearing on the No Wake Zone proposal.

  3. The BOCC holds a public hearing and votes to approve or deny the proposal.

  4. If approved, the County will submit the necessary paperwork to the Wildlife ResourcesCommission.

  5. If approved by the Wildlife Resources Commission, the County will install and maintain buoys identifying the No Wake Zone.

Algal Blooms

Some algal growth is healthy for waterbodies, providing food and habitat for aquatic life and giving off oxygen through photosynthesis.  In some instances, algal growth can be accelerated by excessive nutrients in stormwater runoff, fertilizers and other sources.  Excessive nutrients can lead to rapid reproduction which causes nuisance growths, or blooms.  Algal blooms often occur when conditions are favorable, such as during warm summers with long, sunny days in slow moving or stagnant waters that are rich in nutrients. 

When large amounts of algae die off and decompose in a pond, dissolved oxygen is depleted which can lead to fish kills.  Additionally, some varieties of algae (Cyanobacteria or commonly called blue-green algae) are known to produce toxins which can be harmful to humans and animals when ingested.

Indicators of active cyanobacterial blooms

  • Discolored Water – water may appear bright green/blue-green in color.  When algae begin to die off, water may turn milky blue and produce a strong, foul odor.

  • Surface Scum – some algae form thick scums across the waters’ surface.  They can have the appearance of spilled paint forming a film across the water’s surface.  These scums can accumulate along the shoreline.

  • Flecks and grass clippings – some algae accumulate into colonies observable as blue-green flecks or as clumps that resemble grass clippings. Precautions to take around suspected cyanobacterial blooms

  • ​Keep children and pets away from waters that appear discolored or scummy.

  • Do not handle or touch large accumulations (“sums” or mats) of algae.

  • Do not use scummy water for cleaning or irrigation.

  • If you accidentally come into contact with an algal bloom, wash thoroughly.

  • If your pet appears to stumble, stagger, collapse or uncontrollable vomiting, after being in a pond seek veterinary care immediately.

  • If your child appears ill after being in waters containing a bloom, seek medical care immediately.

Update August 2019 - Ponds in Mecklenburg County which are publicly owned or managed, and which are routinely accessed by the public are currently being screened for the presence of toxic blue-green algae.  In the event that a potentially harmful algal bloom is identified, the appropriate municipality will be notified and requested to install warning signs.   Private pond owners are encouraged to contact a pond management consultant if they have concerns regarding their ponds.  Be aware that ponds are dynamic, continually changing natural environments and are not continually monitored, therefore caution should always be taken around natural water bodies.  The absence of a warning sign does not necessarily mean the pond is safe. 

If you are unsure whether or not a bloom is present, it is best to stay out of the water.

For additional information about algal blooms in NC, visit the​NC Division of Environmental Quality’s website.

For more information on the potential health effects from algal blooms, visit the NC Division of Public Health’s website.


Surface films/discolored water that appears bright green to deep blue-green in color.

​​​Surface films/discolored water.​​    Surface films/discolored water.

Blue and white surface scums associated with decaying blue-green algae.

Surface scum with decaying algae.    Surface scum with decaying algae.

Blue-green flecks and “grass clippings”

Flecks in water.    Grass clippings in water.

Swimming Advisories​

A Swimming Advisory is issued by Charlotte-Mecklenburg Storm Water Services, in conjunction with the Mecklenburg County Health Department, when a natural body of water is considered a public health threat for swimmers. Examples of conditions that may cause an Advisory include a sewage spill, a chemical spill, or unsafe chemical or biological levels identified during routine monitoring. Once an Advisory is issued, the water is typically tested once a day until it is considered safe for swimming.

Although surface water quality is routinely monitored throughout Charlotte and Mecklenburg County, it is impossible to know, at any given time, whether or not water is safe for swimming. The following precautions should always be taken when swimming in natural bodies of water. It is also important to know that typically streams in Mecklenburg County are only suitable for minor contact activities such as fishing and kayaking, but not for swimming. Lake Norman, Mountain Island Lake and Lake Wylie are all considered suitable for swimming.

When a Swimming Advisory is issued or removed, the media is sent a press release, and information is posted below and on Charlotte-Mecklenburg Storm Water Services' Facebook​ and Tw​itterpages.

Swimming​ Advisories ​​​​​​​

Fish Consumption Advisories ​

Fish consumption advisories for Mecklenburg County's lakes are issued by the state and are determined by testing the tissue of the fish. These advisories help people understand if they should limit or completely avoid eating different types of fish. In some cases, advisories are stronger for children or women of child-bearing age. See current fish​ consumption advisories​ affecting Charlotte-Mecklenburg. ​