The Department of Natural Resources and Environmental Control monitors recreational waters to ensure their quality for swimming and other recreational uses. The Department tests for Enterococcus bacteria, which indicate the presence of other potentially harmful bacteria and viruses. The results of these tests are available online and though an email alert system.
Point sources of pollution, and rainfall-driven runoff from the land, known as “nonpoint source pollution,” may introduce disease-causing organisms into swimming waters.
Fortunately, in Delaware, as a result of ongoing efforts to improve the treatment of wastewater and eliminate pollution sources, Delaware’s guarded beaches are no longer impacted by point sources of pollution.
Efforts are also underway to control nonpoint source pollution by installing central wastewater collection and treatment systems to eliminate septic systems and by better managing our agricultural, commercial and residential lands.
Join the Recreational Water Quality email list to get alerts directly. Send a blank email to join-dnrec_beach_monitoring@lists.state.de.us
Recreational water samples are analyzed to determine the levels of Enterococci bacteria. Enterococcus is one of several indicator organisms that signal the presence of potentially harmful bacteria and viruses. Delaware tests the number of Enterococcus colonies found in 100 milliliters of water against a set of standards for issuing recreational swimming advisories at monitored beaches.
The geometric mean is used to determine the long-term safety of a recreational beach for swimming. The instantaneous value allows the Department to assess current water quality conditions. Results are available 24 hours after the sample is delivered to the laboratory. If these standards are exceeded, the Department will use these results, in addition to other factors, to make a decision as to the safety of the waterbody for swimming. A “Swimming Advisory” may be issued.
Delaware Enterococcus Standards
(Colonies per 100 Milliliters of Water)
| Water Type | Geometric Mean | Instantaneous Value | Resample Value |
| Fresh | 100 | 185 | 185 |
| Salt | 35 | 104 | 104 |
Bacteriological water quality can be affected by a number of factors, including human-induced contamination and a number of natural factors. For example, dangerous weather conditions, such as rough surf, can result in samples that do not accurately represent water quality of the beach. Bacteria attached to sediment can be churned up into the water column by wind-induced waves and can also cause dangerous conditions for those collecting the samples. During these events, a resample may be collected as soon as possible.
The State of Delaware has adopted its standards in order to meet the requirements of the US Environmental Protection Agency’s 2012 Recreational Water Quality Criteria.
Related Topics: assessment, clean water, outdoors and recreation, recreational water quality, testing, water, water quality, watershed, watershed stewardship
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