Illinois has 52 public Great Lakes swimming beaches along approximately 60 miles of Lake Michigan shoreline. The Illinois Department of Public Health (IDPH) administers the state's coastal beach monitoring program.
Working to Improve Water Quality at North Point Marina Beach
Beachwater quality at North Point Marina Beach in Lake County has consistently been poor; yearly percent exceedance rates from 2005 to 2011 ranged from 34% to 83%. The Lake County Health Department received Great Lakes Restoration Initiative funding to plant native vegetation, restore the dunes, and remove invasive species. This project is expected to improve water quality and reduce the number of swimming bans at this beach by reducing the seagull population. Work began in spring of this year and is scheduled to be completed by fall of 2013.
Dogs Put to Work Improving Beachwater Quality in Chicago
Two beaches in Chicago, 63rd Street Beach (Jackson Park) and 57th Street Beach, have routinely exceeded water quality standards in the past. Fecal contamination at these beaches is known to be caused at least in part by large numbers of seagulls. Using border collies during the beach season to harass gulls every day from dawn to dusk has proved to be an effective means of improving water quality at these beaches. Gull harassment was implemented in 2008, 2010, and 2011, and the percentage of beachwater samples that exceeded standards in those years was far lower than in years with no gull harassment.
What Does Beachwater Monitoring Show?
In 2011, Illinois reported 62 coastal beaches and beach segments. Of these, 19 (31%) were assigned a monitoring frequency of once a day, 28 (45%) more than once a week, 3 (5%) once a week, and 12 (19%) were not assigned a monitoring frequency.
In 2011, 12% of all reported beach monitoring samples exceeded the state's daily maximum bacterial standard of 235 colonies/100 ml. The beaches with the highest percent exceedance rates of the state standard in 2011 were Winnetka Elder Park Beach in Cook County (54%), North Point Marina Beach in Lake County (34%), Winnetka Centennial Dog Beach in Cook County (29%), Highland Park Moraine Park Dog Beach in Lake County (29%), and Wilmette Gillson Park Dog Beach (29%), Glencoe Park Beach (28%), Rainbow Beach (24%), Montrose Beach (23%), and South Shore (22%) in Cook County. Beaches in Lake County had the highest exceedance rate of the state standard in 2011 (13%), followed by Cook County (12%). NRDC considers all reported samples individually (without averaging) when calculating the percent exceedance rates in this analysis. This includes duplicate samples and samples taken outside the official beach season, if any.
* Please note that only samples from a common set of beaches monitored each year from 2007-2011 are included in the bar chart.
What Are Illinois' Sampling Practices?
The monitoring season extends from Memorial Day to Labor Day.
Samples are taken in water that is knee to waist deep. It is up to the managing entity for each beach to issue swim bans and advisories, depending on EPA guidance and the beach managers' own policies.
Many coastal swimming beaches in Illinois are sampled seven days a week, as Illinois believes daily monitoring is most protective of public health. Areas of shoreline that are not used for swimming because they are rocky or otherwise unsuitable are not monitored. Monitoring on a daily basis is conducted when a swim ban or advisory is issued.
How Many Swim Bans and Advisories Were Issued in 2011?
Total swim ban/advisory days for 325 events lasting six consecutive weeks or less decreased 6% to 476 days in 2011 from 508 days in 2010. For prior years, there were 576 days in 2009, 534 days in 2008, 793 days in 2007, 591 days in 2006, and 585 days in 2005. There were no extended or permanent events in 2011. Extended events are those in effect more than six weeks but not more than 13 consecutive weeks; permanent events are in effect for more than 13 consecutive weeks. For the 325 events lasting six consecutive weeks or less, 95% (450) of swim ban/advisory days were due to monitoring that revealed elevated bacteria levels, 1% (4) were preemptive due to heavy rainfall, and 5% (22) were preemptive to due known sewage spills or leaks.
How Does Illinois Determine When to Warn Visitors About Swimming?
Depending on the managing authority for coastal beaches, both advisories and swim bans are issued. The water quality standard in Illinois is an E. coli single-sample maximum of 235 cfu/100 ml. No geometric mean standard is applied when making swim ban and advisory decisions.
In most jurisdictions, either a swim ban or an advisory is issued if one sample exceeds the single-sample standard. The only exceptions are beaches managed by the Wilmette Health Department (the Gillson Park beaches and Langdon Beach) and the Winnetka Park District (Tower, Maple, and Elder beaches). Two samples are taken daily at these beaches, and if one sample exceeds the standard, a resample is taken before a swim ban is issued. If both samples exceed the standard, a swim ban is issued without resampling. In 2011, the Chicago Park District posted an advisory at its beaches when sample results were between 235 cfu/100 ml and 1,000 cfu/100 ml, and a ban when sample results exceeded 1,000 cfu/100ml. Beginning in 2012, the Chicago Park District is posting advisories when sample results exceed 235 cfu/100 ml and bans when there is a sewage spill.
Beach managers may preemptively issue swim bans or advisories because of rain or other factors.
The managers of Waukegan South Beach, Forest Park Beach in Lake Forest, and Rosewood Beach in Highland Park in Lake County use a predictive model called SwimCast to make swim ban and advisory decisions. At a minimum, predictions are generally made at 9 a.m. and 1 p.m. and whenever hydrometeorological conditions change. For each beach where the SwimCast system exists, similar but slightly different predictive models are utilized. These models predict beachwater conditions on a real-time basis, in contrast to standard culture methods for quantifying bacteria. When culture methods are used as the basis for issuing swim bans and advisories, health warnings are not issued until at least 24 hours after samples are taken due to the time required to process and read the samples. In a sense, using culture methods to issue swim bans and advisories is akin to using yesterday's bacteria density to predict today's bacteria density. Studies have shown that SwimCast provides a more accurate assessment of current beachwater quality than does the prior day's bacterial density.
SwimCast models produce a 99% confidence interval—that is, a lower and upper bound of bacterial concentrations between which the actual bacteria concentration is expected, with 99% confidence, to lie. At all beaches where the SwimCast model is used, the determination of swim bans and risk advisories is the same:
- A swim ban occurs when the lower bound of the 99% confidence interval prediction is above 235 cfu/100 ml. Under a ban, the beach is posted with a red flag. This is the highest-risk condition.
- When the average prediction and upper bound of the 99% confidence interval prediction are above 235 cfu/100 ml but the lower bound is below 235 cfu/100 ml, this is considered to be a moderate- to high-risk condition and is posted as an advisory at the beach.
- When the upper bound of the 99% confidence interval prediction is above 235 cfu/100 ml but the average prediction and the lower bound of the 99% confidence interval prediction are below 235 cfu/100 ml, this is considered to be a moderate-risk condition and is posted as an advisory at the beach.
- When the upper bound of the 99% confidence interval prediction is below 235 cfu/100 ml, this is considered to be a low-risk condition and is posted with a green flag.
In the Chicago Park District, intensive data collection began in 2011 for model development at five additional beaches: Foster, Montrose, Oak Street, 63rd Street, and Calumet. The District is using models at several of these beaches to make swim ban and advisory decisions in 2012.
Illinois 2011 Monitoring Results and Notice and Advisory Days
||Assigned Monitoring Frequency
||% of samples exceeding state standards
||Closing or Advisory days