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2014 Mecklenburg County State of the Environment Report

Lake Intended Use: How Good is the Water?

indicatorWater quality in Charlotte-Mecklenburg's three lakes generally meets the state standards for the‚Äčir intended uses which include recreation and supplying drinking water. Overall water quality is very good and the trend remains stable.

LUSI chart 

Lake Intended Uses
Lake Norman, Mountain Island Lake, and Lake Wylie cover more than 47,000 acres. Together, the three lakes bordering Charlotte-Mecklenburg hold about 465 trillion gallons of water. The water quality of the three lakes meets state standards for the lakes' intended uses. The NC Division of Water Quality has classified the lakes as Class B and WS-IV waters for use by residents, industry and supplying drinking water. The lakes provide approximately 110 million gallons of drinking water each day to Charlotte-Mecklenburg.

Water quality in our lakes
Based on the Lake Use-Supported Index (LUSI) developed by Charlotte-Mecklenburg Storm Water Services, the overall water quality downstream of Charlotte-Mecklenburg at Lake Wylie is very good; it improves upstream at Mountain Island Lake, and improves still further upstream at Lake Norman. The LUSI data represented in SOER 2014 differs from previous SOER reports in that the SOER 2012 LUSI illustrated only data from monitoring sites located in coves within Mecklenburg County. Cove water quality data continues to show an improving trend. For SOER 2014 we have included data from all of our lake monitoring sites including several main channel sites. This provides a better overall picture of water quality conditions throughout the lake, but has had a stabilizing effect on the previously reported upward trend. When including data from all lake monitoring sites, the trend since 2012 is basically stable (flat) and within the Good/Excellent range.

What we look for
LUSI is based on various water quality parameters. Each parameter is an independent measure of water quality, with fecal coliform being the most important indicator of swimmability. Fecal coliform bacteria levels are usually low in the three lakes, except in coves after significant storm events. Bacteria levels that exceed North Carolina water quality standards can directly impact the health of swimmers.

Sources of fecal coliform include sanitary sewer spills and waste from domestic pets, farm animals and wildlife. Fecal bacteria can be reduced or controlled by:
  • maintaining intact lake buffers
  • agricultural BMPs
  • pet waste pickup
  • sanitary sewer system maintenance (inspection and cleaning)
  • regular septic system maintenance

Although overall water quality is determined by a combination of many factors, fecal coliform is the single biggest indicator of swimmability and recreational suitability.

Fish consumption advisories
The bioaccumulation of toxins in fish tissue due to prolonged exposure to pollutants has resulted in the issuance of advisories by the State on the number of fish that are safe for human consumption. More about fish consumption advisories on local lakes.

For more information contact:

More information

Return to Water Chapter Page 

The trends shown in the State of the Environment Report are not all based on tests of statistical significance. Data analysis, anecdotal evidence, and best professional judgment have been compiled to represent these trends. The State of the Environment Report takes a snapshot of important environmental indicators in an effort to educate the public while highlighting challenges, successes and the general direction of change for each indicator. For additional information on these indicators and the determination of trends, please follow the links and feel free to contact the appropriate resources.

Last updated 2/20/14