Hull, MA - 06/05/14 Features. Rain didn't stop this surfer from taking to the water off Hull's Nantasket beach. - (Barry Chin/Globe Staff), Section: Metro, Reporter: In caps, Topic: xxFeature, LOID: 5.0.1725229525.
Rain didn't stop this surfer from taking to the water off Hull's Nantasket beach.
BARRY CHIN/ THE BOSTON GLOBE

How does your beach’s water quality stack up?

Save the Harbor/Save the Bay, a non-profit harbor advocacy organization, just released its third annual Beach Water Quality Report Card on Boston Harbor Region’s public beaches. All the beaches survey are managed by the Department of Conservation and Recreation (DCR).

According to the report card, there were thousands of water samples taken at the beaches in 2013 and “the samples were collected at 34 testing sites on public beaches in Nahant, Lynn, Swampscott, Revere, Winthrop, East Boston, South Boston, Dorchester, Quincy and Hull.”

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The results of “Overall Beach Safety” are based on 2013 data:

1. Nantasket 100%

2. City Point 100%

3. Savin Hill 100%

4. Carson Beach 98.73%

5. M Street 98.73%

6. Constitution Beach 97.05%

7. Pleasure Bay 95.78%

8. Short Beach 94.12%

9. Winthrop Beach 94.12%

10. Revere 93.75%

11. Nahant 91.18%

12. Wollaston* 88.27%

13. King’s Beach**83.12%

14. Malibu Beach 76.47%

15. Tenean Beach 62.96%

Wollaston Beach includes the Milton St, Channing St, Sachem St, and Rice Road sampling locations. King’s Beach has 3 primary sampling locations, but is also tested at Stacey Brook outfall for bacterial exceedances.

According to the executive summary of the water report card there are a variety of considerations taken when analyzing water quality: Enterococcus (microbial indicator of GI illness used in marine waters), geometric mean (bacterial exceedance values from the previous five days without rain).

Then they also take in to account Beach Flagging and Management which includes: sensitivity (when the beach has a red flag and is not safe for swimming), positive predictive efficiency (what fraction of the time a posted red flag is correct), specificity (when the beach is safe for swimming, what fraction of the time the beach is correctly labeled with a blue flag), negative predictive efficiency (fraction of time when a posted blue flag is correct), and overall predictive efficiency (what fraction of the time the flags are in general correct).

All beaches had a percentage of 91.62% for 2013 overall beach safety.