The Swimmability Index

Purpose

To assess fecal contaminant` levels in nearshore recreational waters by using a surrogate indicator for pathogen types causing potential harm to human health through body contact with nearshore recreational waters.

Goal

Waters should be safe for recreational use. Waters used for recreational activities involving body contact should be substantially free from pathogens, including bacteria, parasites, and viruses, that may harm human health. This indicator supports Annexes 1, 2 and 13 of the Great Lakes Water Quality Agreement.

Status

Currently, there are two methods recommended for beach water quality monitoring: counts of either E. coli and/or enterococci in recreational waters measured as number of organisms per volume of water (e.g., EC/100 ml). When the bacteria standards are exceeded, local authorities may ban swimming at a beach or issue an advisory that water is unhealthful for swimming.  In the rest of the text, we'll use the term "posting" to describe either of these two actions.  A small number of postings may be due to weather conditions (lightning, high water).

Frequency of swimming advisories or closings at specific locations are reported annually and become the basis of a "Swimmability Index" (the percent of swim season individual beaches have not been posted due to bacterial contamination and/or other environmental condition, including pre-emptive postings based on past experience).

The Beaches Environmental, Assessment, and Coastal Health (BEACH) Act of 2000 aims to protect beach-goers from disease-causing pathogens by establishing a national baseline for beach water quality and by providing grants to states to develop and implement water quality monitoring and public notification programs. A health risk assessment based on the number of days a beach is posted is suggested. A beach that is not posted during the swimming season has low risk. A beach that is posted 10% or more days during the swimming season has high risk. Beaches posted for one day or more but fewer than ten days (swimming season in the Great Lakes is defined as June to August) are characterized as medium risk. 

Survey reports of postings during the 1998 swimming season (June, July, August) show that 75% of the respondents conducted some form of monitoring (see table below) and 70% were open for the entire 1998 season (see pie-chart below).

Survey reports of beach postings during the 1999 swimming season (June, July, August) show that 75% of the respondents conducted some form of monitoring (see table below) and 70% were open for the entire 1999 season (see pie-chart below).

Survey reports of beach postings during the 2000 swimming season (June, July, August) show that 71% of the respondents conducted some form of monitoring (see table below) and 68% were open for the entire 2000 season (see pie-chart below).

Survey reports of beach postings during the 2001 swimming season (June, July, August) show that 71% of the respondents conducted some form of monitoring (see table below) and 74% were open for the entire 2001 season (see pie-chart below).

Survey reports of beach postings during the 2002 swimming season (June, July, August) show that 79% of the respondents conducted some form of monitoring (see table below) and 66% were open for the entire 2002 season (see pie-chart below).

Beach postings and monitoring practice was not reported by USEPA in 2003. 2003 beach information (Testing the Waters 2004: A Guide to Water Quality at Vacation Beaches) can be found at the National Resource Defense Council Web site http://www.nrdc.org.

Survey reports of beach postings during 2004 swimming season (June, July, August) show that 79% of the respondents conducted some form of monitoring (see table below) and 72% were open for the entire 2004 season (see pie-chart below).

Presenting the 1998 data in bar chart form, arranged by number of days a beach was posted emphasizes the large number of beaches reporting little or no pollution closings, while, at the same time, the relatively few beaches reporting long duration closings. Duration of advisory or closing was calculated by subtracting the start date of the advisory from the end date. In the case where the start and end date were the same date, the duration was entered as one day.

Presenting the 1999 data in bar chart form, arranged by number of days a beach was posted emphasizes the large number of beaches reporting fewer postings.  However, more beaches were reporting longer duration closings. This apparent increase in beach postings may be due to two causes. One: the increased use of E. coli as the action indicator by beach managers, and two, a change in reporting the length of a closing or advisory. The survey requested that the public health agency provide the duration of the advisory or closing. This change in reporting resulted in more two day durations which would have been calculated as one day durations using the 1998 procedure.

Beaches reported to have longer-term and repeated swimming closings over a period of years can be identified and considered for remediation.

Presenting the 2000 data in bar chart form, arranged by the number of days a beach was posted emphasizes the large number of beaches reporting fewer postings.  However, the number of beaches reporting longer durations is almost double the average number reporting longer duration from the two previous years.  The cause of these closures is not clear at this point, but similar results have been reported for all beaches in the Natural Resources Defense Council report, Testing the Waters 2001.  Beach closures have increased following better testing and reporting.

During 2001, 9 of the beaches posted for 10 days or more of the 92-day Great Lakes swimming season were identified as high priority beaches by Region 5 state agencies. These are identified below, giving number of days closed, beach name, county, state, and cause of closing.

Presenting the 2001 data in bar chart form, arranged by the number of days a beach was posted emphasizes the large number of beaches reporting fewer postings. The number of beaches which have been reported open all season is the highest in the last four years. The number of beaches reporting more than 10 % of the swimming season with postings continues to be approximately twice what was reported prior to 2000. Beach postings have increased following better testing and reporting, which provides better swimmer protection at the beaches where monitoring is conducted.

During 2002, sixteen of the beaches posted for 10 days or more of the Great Lakes swimming season (June, July, August) were identified as high priority beaches by USEPA Region 5 State agencies. These are identified in the table below.

Presenting the 2002 data in bar chart form, arranged by the number of days a beach was posted emphasizes the large number of beaches reporting fewer postings.  Again this year, more beaches reporting being open all season is a record high for the last five years.

During 2004, one hundred and seven beaches were posted for 10 days or more of the Great Lakes swimming season (June, July, August). One of these beaches was closed permanently. Ninety one red beaches were ranked as State high priority (Tier 1) beaches. Red beaches were located in all the Great Lake basins and in every state except Indiana and Pennsylvania. The median monitoring effort for a red beach was five times per week, but ranged from one time per week to seven times per week. The average monitoring effort was 3.9 times per week. The most frequently cited source for postings was unknown for 85 of the beaches. Storms were cited as the sole cause of postings at 17 beaches. The increase use of “unknown source” for the closings in 2004 by nearly all the states may be due to the change in method of reporting required by the BEACH Act. Previous responses by beach managers used “unknown source” 13% in 2001 and 26% in 2002 respectively. If the sources of posting is not know, it indicates the critical need for sanitary surveys to determine the source of pollution at these beaches where postings are exceed 9% of the swimming days.

Presenting the 2004 data in bar chart form, arranged by the number of days a beach was posted emphasizes the large number of beaches reporting fewer postings. In 2004, more beaches were reported open during the months of June, July, and August. This is a record high since reporting began in 1981 primarily due to increased monitoring and reporting resulting from BEACH Act money available to the states.

The percentage of beaches reporting postings for more than 10% of the swimming season remains at around 12 to 14% and continues to be approximately twice what was reported in 1999 and comparable to the last two years. The percentage of  beaches open all season is the highest since 2001 (see figure below).

Trends