Lake by lake
Resources and references
About the Great Lakes LaMPs study...
Glossary of terms
Lake Michigan, the second largest Great Lake by volume with 1,180 cubic miles of water, is the only Great Lake entirely within the United States. Approximately 118 miles wide and 307 miles long, Lake Michigan has more than 1,600 miles of shoreline. Averaging 279 feet in depth, the lake reaches 925 feet at its deepest point. The lake's northern tier is in the colder, less developed upper Great Lakes region, while its more temperate southern basin contains the Milwaukee and Chicago metropolitan areas. The drainage basin, approximately twice as large as the 22,300 square miles of surface water, includes portions of Illinois, Indiana, Michigan, and Wisconsin. Lake Michigan is hydrologically inseparable from Lake Huron, joined by the wide Straits of Mackinac.
Localized outbreaks of water-borne disease have been linked to contamination by bacteria or viruses, probably from human or animal waste. Recently, there has been increasing concern over the presence in drinking water of parasites such as Giardia and Cryptosporidium (the most common source of which is animal feces), which are resistant to common disinfection practices, and may pass through water treatment filtration and disinfection processes in sufficient numbers to cause health problems. For example, in 1993, the city of Milwaukee, Wisconsin, experienced an outbreak of cryptosporidiosis that affected over 400,000 residents, causing severe diarrhoea, nausea, stomach cramps, and other symptoms. The outbreak was caused by Cryptosporidium oocysts that passed through the filtration system of one of the city’s two water-treatment plants.
Cryptosporidium is a one-celled parasite that is spread through human or animal fecal contamination. When the organisms are ingested, they cause an infection and irritation of the digestive track that leads to acute diarrhea. For healthy people, this is generally a short term condition. However, it can be an extremely dangerous for small children and adults with Acquired Immune Deficiency Symdrome (AIDS), cancer, or other health problems. There is no effective drug for the treatment of cryptosporidiosis and currently it is not known whether any concentration of the organisms is safe for human consumption.
Cryptosporidium poses a greater hazard than other potential pathogens in drinking water supplies because of its ability to withstand traditional drinking water treatment. Individual organisms form small hard shelled oocysts when in hostile environments such as surface water. These oocysts are resistant to chlorine and small enough to evade most filter technologies. However, since the Milwaukee outbreak, EPA has strengthened turbidity requirements for finished tap water, to ensure better filtration methods. However, even in water meeting the new standards, small numbers of oocysts may still breach filters.
Food, including fish consumption, is the primary route of exposure to persistent, bioaccumulative and toxic chemicals, including PCBs and mercury. For the U.S. Great Lakes basin, measured levels of these persistent toxic chemicals in drinking water are below the Maximum Contaminant Levels (MCLs) and therefore they are not considered to be a human health concern for drinking water.
Although there have been sporadic outbreaks of illness related to the use of drinking water, the drinking water in the Lake Michigan basin is of good quality. However, continuing efforts must be made to inform health professionals and the public of the results of analyses of drinking water. Information on local water quality is available from several sources, including the state public health department and local water supplier.
The EPA requires public water supplies to be monitored for bacteriological, inorganic, organic and radiological contaminants. The chemical analyses of drinking water include physical and chemical characteristics of the water, as well as contaminants resulting from natural sources or human activities. Community water suppliers deliver high quality drinking water to millions of people every day, and a network of government agencies are in place to ensure the safety of public drinking water supplies. Our drinking water is safer today than ever but problems can, and do occur, although they are relatively rare.
It is important to note that most shoreline areas along Lake Michigan fully support all forms of water-based recreation, including swimming, boating, and wading. However, some areas do experience closures due to contamination. Beach closings resulting from high pathogen loads have a tremendous negative effect on the tourist industry. In 1996, for example, visitors to the Indiana counties bordering Lake Michigan spent over $523 million and beach closings can cost an area up to $5 million per day in lost revenue.
Federal and State recreational water quality guidelines recommend bacterial levels below which the risk of human illness is considered to be minimal. For public beaches along Lake Michigan, the regional Health Departments generally monitor beach water quality. In Chicago, for example, the Chicago Park District conducts beach water quality monitoring. When contaminant indicator levels in the bathing beach water reach levels that are considered to pose a risk to health, public beaches may be posted with a sign warning bathers of these potential health risks.
A number of initiatives have recently been developed to specifically address recreational water quality. The U.S. EPA established the Beaches, Environmental Assessment, Closure, and Health Program (BEACH) in 1997 to "significantly reduce the risk of waterborne illness at the nation's beaches and recreational waters through improvements in recreational water protection programs, risk communication, and scientific advances."
Under the BEACH Program, the first National Health Protection Survey of Beaches, conducted in 1997, focused on the collection of beach-specific information from coastal and Great Lakes states. Data from the other annual surveys, conducted in 1999 and 2000, are now accessible. EPA will also develop a national inventory of digitized beach maps which will be linked with locations of pollution sources through a Geographic Information System (GIS).
The number of recreational boats operated on Lake Michigan each year is estimated at 400,000, or nearly half of the number for all the Great Lakes. Although boating has a strong connection to fishing, which relies on clean water and productive fish stocks, much of the boating activity is tied to marina and new residential development, which alters nearshore habitat and degrades water quality in localized areas.
Around the southern shore of Lake Michigan, about 1,000 new slips were added per year in the late 1980s and early 1990s. In Indiana, for example, Lake Michigan boat slips increased from 1,100 in 1985 to 2,700 in 1991, though many new marinas in Indiana are being built on previously developed sites.
Studies have shown that swimmers and people engaging in other recreational water sports have a higher incidence of symptomatic illnesses such as gastroenteritis, otitis, skin infection, conjunctivitis, and acute febrile respiratory illness (AFRI) following activities in recreational waters. Although current studies are not sufficiently validated to allow calculation of risk levels, there is some evidence that swimmers and bathers tend to be at a significantly elevated risk of contracting certain illnesses (most frequently upper respiratory or gastro-intestinal illness) compared with people who do not enter the water. In addition, children, the elderly, and people with weakened immune systems are those most likely to develop illnesses or infections after swimming in polluted water.
Despite these studies, there are challenges in establishing a clear relationship between recreational water exposure and disease outcomes. Less severe symptoms resulting from exposure to microorganisms are not usually reported, which makes statistics on cases related to recreational water exposure difficult to determine. In addition, the implicated body of water is not often tested for the responsible organism and when it is tested the organism is not usually recovered from the water. With the exception of gastro-intestinal illness, a direct relationship between bacteriological quality of the water and symptoms has not been shown -- a causal relationship exists between gastrointestinal symptoms and recreational water quality as measured by indicator-bacteria concentration. Therefore, research efforts are focusing on conducting epidemiological studies to better establish the relationships between diseases and the presence of microorganisms in the water.
Last modified: April 29, 2003