Water Quality

The watersheds that surround Oak Island stem from two main river basins:  the Lumber River basin to the west that empties out through Lockwood Folly and the Cape Fear River basin to the east.  A brief overview of each river basin is provided below followed by a summary of the water quality data.

Lumber River and Cape Fear River Basins

As noted above, Brunswick County encompasses both the Lumber and the Cape Fear River Basins.  The Lumber River comprises approximately 55% of the western portion of the county while the Cape Fear River occupies the remaining 45% of eastern Brunswick County.  The Cape Fear River basin itself is comprised of 24 sub-basins as depicted below in Figure 1.  (For a better view of the maps below, click on the image.) 

Details of the hydrologic features, ecosystems, and impact on water quality are provided in the October 2005 Cape Fear River Basinwide Water Quality Plan.

The Lumber River Basin lies along the North Carolina-South Carolina border extending 150 miles from the Sandhills region in southern Moore and Montgomery counties to the Atlantic Ocean.  It is comprised of 10 sub-basins, all of which empty into South Carolina's Pee Dee River except for Lockwood Folly and the Shallotte River.

The Lumber River basin is composed of three distinct ecological regions:  the Sandhills, the Carolina Bay region, and the Southeastern Coastal Plain, all of which gives it an exceptional biological diversity from the pocosins of the Green Swamp to the Lake Waccamaw area to the dry sandy hills of coastal Carolina with longleaf pines.  Of particular note are the wetland ecosystems associated with blackwater river floodplains and pine savannas. 

Details of hydrologic features, ecosystems, and impact on water quality are provided in the 2007 Lumber River Basinwide Water Quality Plan.    

Water Quality Monitoring Data and Reports

Downstream portions of both Lockwoods Folly and Shallotte River are designated SA (waters designated for shellfish harvesting) and are therefore, High Quality Waters.  Most waters in these sub-basins have fecal coliform counts above state standards (per the NC Administrative Code 15A NCAC 02B.0221), which are summarized in the table below.

Table 1:  Summary of State Water Quality Standards for Tidal Salt Water Class SA Waters

The water quality standards for High Quality Waters (per NC Administrative Code 15A NCAC 02B.0224) are summarized in the table below.

Table 2:  Summary of State Water Quality Standards for High Quality Waters (HWQ)

Monitoring for Cape Fear River is conducted by a number of different state and local organizations.  The University of North Carolina at Wilmington (UNCW) Center for Marine Science has prepared annual reports on the lower Cape Fear River since 1995.  The 2004-2005 report noted all stations as good in terms of chlorophyll a, except for Station PB, which was rated fair.  For turbidity 100% of the sites were rated good.  However, 22% of the stations had either fair or poor water quality in terms of fecal coliform bacterial contamination.  Using the 5.0 mg/L DO standard for the Piedmont river stations, and the 4.0 mg/L “swamp water” DO standard for the stream stations and blackwater river stations, 41% of the sites were rated poor or fair for dissolved oxygen.  In addition, UNCW considered 60% of the stream stations to be negatively impacted by excessive nitrate and 10% of the stream stations negatively affected by excessive total phosphorus concentrations. 

The sum of these monitoring reports indicate water quality is declining for the area surrounding Oak Island, largely as an impact from development.  The water quality standards that Oak Island is required to maintain are detailed in the Town of Oak Island's 201 Facilities Plan Update.  The impact of further decline in water quality could likely lead to a state-mandated monitoring program (e.g., TMDL) for key pollutants and the potential for additional mitigation if SA waters and HWQ waters do not improve.

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