Collected date Tier Enterococci (per 100mL of water)
Single sample MPN Geometric Mean MPN Single sample CFU Geometric Mean CFU
Apr 10, 2024 9:30 AM 2 10
Feb 15, 2024 10:03 AM 2 10
May 15, 2024 9:33 AM 2 9
Mar 13, 2024 10:38 AM 2 20
Apr 10, 2024 9:52 AM 2 9
Apr 18, 2024 10:21 AM 2 9
May 1, 2024 9:14 AM 2 10
Apr 17, 2024 9:52 AM 2 9
Mar 13, 2024 10:33 AM 2 9
May 15, 2024 9:42 AM 2 9
Apr 10, 2024 9:46 AM 2 10
May 15, 2024 9:44 AM 2 10
Feb 15, 2024 10:53 AM 2 406
May 22, 2024 9:36 AM 2 9
Jun 12, 2024 9:37 AM 2 9
May 1, 2024 9:23 AM 2 10
May 1, 2024 9:20 AM 2 10
Jun 5, 2024 9:40 AM 2 9
Mar 13, 2024 10:51 AM 2 10
May 22, 2024 9:41 AM 2 9
Feb 26, 2024 9:41 AM 2 9
Jun 5, 2024 9:58 AM 2 9
Apr 18, 2024 10:02 AM 2 10
Mar 13, 2024 9:55 AM 2 9
Apr 10, 2024 9:12 AM 2 9
Jun 5, 2024 10:00 AM 2 9
Apr 17, 2024 9:46 AM 2 9
Apr 18, 2024 10:10 AM 2 9
Feb 15, 2024 10:12 AM 2 9
Apr 18, 2024 9:26 AM 2 9
Apr 18, 2024 10:00 AM 2 9
May 15, 2024 11:20 AM 2 9
Apr 24, 2024 9:30 AM 2 9
Jun 5, 2024 9:50 AM 2 9
Mar 13, 2024 10:41 AM 2 9
Jan 11, 2024 10:01 AM 2 9
Jan 3, 2024 10:59 AM 2 9
Apr 16, 2024 10:04 AM 2 10
May 15, 2024 9:23 AM 2 9
Apr 11, 2024 9:15 AM 2 20
Feb 15, 2024 9:53 AM 2 9
Mar 13, 2024 11:31 AM 2 9
Jan 3, 2024 10:14 AM 2 10
May 15, 2024 9:30 AM 2 9
May 8, 2024 8:52 AM 2 10
Jun 12, 2024 9:42 AM 2 9
Jun 5, 2024 10:38 AM 2 9
Jan 3, 2024 10:23 AM 2 10
Mar 13, 2024 10:31 AM 2 10
May 1, 2024 9:33 AM 2 10
Jun 5, 2024 11:27 AM 2 99
Jun 18, 2024 10:20 AM 2 9
May 1, 2024 10:44 AM 2 10
Jan 11, 2024 9:51 AM 2 31
Feb 26, 2024 9:35 AM 2 9
Jun 5, 2024 9:47 AM 2 9
Jan 3, 2024 10:11 AM 2 31
Apr 18, 2024 10:07 AM 2 9
Apr 10, 2024 10:04 AM 2 9
Mar 27, 2024 9:30 AM 2 10
Apr 24, 2024 9:38 AM 2 9
Jan 3, 2024 10:22 AM 2 10
Apr 10, 2024 9:48 AM 2 222
Feb 15, 2024 9:54 AM 2 9
Feb 15, 2024 9:16 AM 2 10
May 15, 2024 10:20 AM 2 9
Jan 3, 2024 11:08 AM 2 31
May 8, 2024 8:47 AM 2 10
Mar 27, 2024 9:25 AM 2 9
Apr 10, 2024 9:55 AM 2 9
Feb 15, 2024 10:00 AM 2 31
Jan 3, 2024 10:06 AM 2 10
May 1, 2024 9:32 AM 2 9
May 1, 2024 10:09 AM 2 9
What is "enterococcus?"
Enterococcus (plural "enterococci") is a bacterial organism commonly found in the intestinal tracts of warm-blooded animals. The N.C. Recreational Water Quality Program's staff measure levels of enterococci in water samples and issue swimming advisories when those levels exceed established limits.
What is a "beach tier?"
In accordance with the federal BEACH act and associated guidance provided by U.S. Environmental Protection Agency, the program ranks beaches into tiers according to average public use. This ranking determines the criteria for whether an advisory is issued based on sampling results. North Carolina's tier structure is summarized in the table below:
Classification Average use Frequency Single-sample max Geometric mean # of sites
(enterococci per 100mL of water)
Tier 11 Daily 104 35 137
Tier 2 3 times / week 276 -- 41
Tier 3 4 times / month2 500 -- 31
What is a "single sample maximum?"
The program's laboratory analyzes each water sample collected so that an estimate of the number of enterococci cells contained therein can be determined. This estimate is defined as a single sample most probable number, or MPN. A swimming advisory is issued when the single sample MPN exceeds the single sample maximum, as determined by beach tier. A colony forming unit, or CFU, is a direct count of the enterococci organism and is not an estimate.
What is a "geometric mean?"
A geometric mean is a kind of mathematical average. The program's staff maintains a running monthly geometric mean of five sample MPN values collected in 30 days. At the present time, both the monthly geometric mean and the single sample maximum are used as criteria for Tier 1 beaches only. For other tier classifications, the single sample maximum is the sole criterion.