Beach Ratings Explained
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NRDC selected five criteria for rating beaches across the country. Beaches received one star for each of the standards they met. Here are the criteria that we used and an explanation of why they are important indicators of beachwater quality and the level of protection offered to beachgoers:
Of the water samples taken during the 2007 monitoring season, fewer than 5 percent exceeded the national health standard for bacteria.
This beach rarely, if ever, had water quality that violated the standard. An adequately monitored beach whose water is consistently meeting the national standard is a smart choice for beachgoers looking for a safe and healthy swim. Some states have standards that are even more stringent than the national guidelines, so making sure that those standards are also being met is a good idea.
The national health standard for bacteria was exceeded in less than 5 percent of the samples taken every year for the last three years (2005-2007).
For the third year in a row, NRDC calculated percent exceedance of the national health standard for water samples from our nation’s beaches, and for the first time this year has taken a look at the emerging trend. Although we applaud those beaches that almost always met the health standard in 2007, beaches with a history of rarely, if ever, being in violation deserve special recognition. Water quality can fluctuate from year to year depending, for example, on the amount of rainfall, particularly at beaches most susceptible to stormwater contamination. The best beaches are those that meet public health standards during both wet and dry years.
Beach location was monitored more than once a week.
The federal BEACH Act requires Tier 1 (most popular or most likely to be polluted) beaches to be monitored at least once a week. Although this is the minimum, unless beaches are being monitored more frequently, beachgoers cannot be sure they are safe when they want to swim. For example, if a beach is tested on Monday and is found to be safe, that does not indicate what the water will be like on Saturday when visitors crowd the shores. Beaches that are monitored more frequently are more protective of beachgoers.
Closings or advisories are always issued without waiting for resampling or other information to confirm results.
Beachgoers need to be notified when their beach is in violation of the health standard, and they should get this information as soon as initial results are in. In some states, beachwater managers usually resample or gather other information before issuing an advisory, while other beachwater managers do this only when they have reason to doubt the results. Waiting for an exceedance to be confirmed before notifying the public puts swimmers at unnecessary risk. This is especially true given the lag time of 24 hours or more that it currently takes before test results are in, leaving a dangerous window when swimmers can be exposed to harmful pathogens.
Both the single-sample maximum and the geometric mean are considered when making closing and advisory decisions.
According to BEACH Act guidelines, states may use the single sample maximum (SSM) for making closing and advisory decisions. The SSM allows beach managers to act quickly to short-term changes in water quality and helps those who have insufficient sample points to calculate the geometric mean (GM). Although the SSM is useful in closing and advisory decisions, the GM a useful complement because it is less subject to random variation -- indicative of recurring contamination issues -- and more directly linked to the studies on which the health standards are based. Beach managers should be sampling frequently enough to use both of these measures and should act to protect the public when there is an exceedance of either.
