We conduct bathing beach sampling every summer during June through August. The water is tested for E-coli bacteria and judged against limits established by state law.

Public beaches are tested annually, on a weekly basis during June through August. Public beaches sampled every year include government owned beaches (state, county, and city parks), commercial beaches (pay-to-swim beaches, country clubs, etc.), beaches at educational institutions and foster care homes, and children's camp beaches.

If you live on lakefront property and choose to swim right at your house rather than at an established beach area, you need to know that the bacteria results from the beach area do not necessarily correspond to where you are swimming. Concerned homeowners that swim at private beaches are encouraged to conduct their own bacteria sampling. The procedure is very easy and our laboratory only charges $12 for a sampling kit as long as:

1. You are an Oakland County resident
2. The source water to be tested is located within Oakland County, and
3. The area to be sampled is a beach or intended for swimming. You may call our office and request a copy of our surface water sampling guidelines if you are interested.

If you are conducting some sampling of your own, you will need to know the E-coli limits and the sampling schedule. It is important to understand that random, individual samples are not a reliable indicator of water quality. We are required by law to take a minimum of three samples each time we test a particular beach area. We will then calculate a daily geometric average (different from a normal arithmetic average) from those three samples, which must be below 300 E-coli to be considered safe for swimming.

Sometimes one or two of the samples may be above 300, but the daily geometric average is below 300, so the beach is not closed. Also, if you want to get an accurate idea of your beach's overall water quality, you must sample on more than one occasion.

The law requires a minimum of five sampling events (consisting of at least three samples per event) within a 30-day period to be considered a valid and reliable study of the water quality. After 30 days you need to calculate a seasonal geometric average for all of your individual samples within that time frame. This seasonal geometric average must be below 130 E-coli to be considered safe for swimming.

It is a popular misconception that if one area of the lake is contaminated, then the whole lake is contaminated. This is not true.

Bacteria contamination originates from conditions or factors present on or near the shore in the immediate vicinity of the beach. Two beaches on opposite ends of a lake that have different on-shore conditions will not have the same bacteria levels. This is why it is important for private homeowners who swim near their house to periodically take samples from where they swim and not rely on results from a beach down the road. Since contamination originates on-shore, it is generally considered to be safer in deeper areas away from the shoreline because wind direction and wave action could trap bacteria against the shore.

Quantitative Polymerase Chain Reaction, or qPCR, is a laboratory technique measuring E. coli DNA. The goal of qPCR is to allow for the Health Division to provide the public with quicker results. Compared to Colilert (the method used at all beaches and the test that triggers a beach closure), qPCR results are ready within four hours while Colilert results are not available until the next morning. More work is being done to ensure qPCR methods are as protective as Colilert in Oakland County's inland lakes. 

Click here for more information about qPCR.

Due to state water quality standards, only Colilert results may be used to issue a beach closure. With the quicker results from qPCR, the Health Division will issue an advisory recommending beachgoers avoid swimming. The following day, the advisory will either be lifted or the beach will be closed, depending on the Colilert results. Click here for more information about qPCR.