MMSD Freshwater Resources Monitoring
Annual Summary Report 2022
The Freshwater Resources Monitoring group conducts routine surface water monitoring at nearly 100 fixed monitoring sites within the MMSD Planning Area and Lake Michigan. Field measurements and grab samples are taken at these sites in all weather conditions and brought to the in-house certified laboratory to be analyzed for almost over 40 different parameters.
To summarize the large amount of data collected each year, the Freshwater Resources Monitoring group produces an annual report that highlights a specific subset of parameters and/or sites. The parameters highlighted in this report have numeric criteria established by the WDNR and are common pollutants in the region.
The interactive map below shows the percent of samples meeting surface water quality criteria at monitoring sites in 2022. Click on the buttons on the left to explore results from the following measured parameters.
Despite relatively good overall compliance for chloride and dissolved oxygen at our sampling sites in 2022, the truth is that both of these parameters continue to be a concern in this region.
Due to the high variability of chloride and dissolved oxygen in a stream, it is important to look further into the data. Temperature, precipitation, and local inputs can dramatically change chloride and dissolved oxygen levels in a very short time frame for both the better and worse. Looking at a minimum for dissolved oxygen and maximum for chloride can provide a better picture of the health of a stream. For these two parameters, the criteria that compliance is based off of represents imminent danger to aquatic life. Exceeding this criteria for a short period even just once in a year can have dire consequences for fish and the food web they depend on.
Across all 91 sites during the warmer months (i.e. May-September), all but one chloride sample met surface water criteria. In the colder months, the story is very different. Numerous sites have chloride concentrations that exceed the criteria which all occurred in the colder months (i.e. October-April). In the most extreme cases, these concentrations can be up to ten times larger than a typical concentration collected at the same site during the warmer months of the year.
30% of the sites had at least one dissolved oxygen result that was not in compliance with surface water criteria. Five monitoring sites had dissolved oxygen levels below 2 mg/L, meaning that aquatic life cannot be supported.
Chloride concentration tends to be seasonal, with highest concentrations during and after snowmelt due to runoff after salt usage. Aquatic life can be sensitive to acute (short-term) exposure to chloride so it is important to look at the highest concentration.
Dissolved oxygen levels tend to be seasonal, with lowest levels during warm and dry weather. Aquatic life can become stressed and die within a short time frame when exposed to low dissolved oxygen levels in the stream. Maintaining a minimum dissolved oxygen level is important to sustain a healthy aquatic system.
MMSD is dedicated to upholding its mission of protecting public health and the environment. MMSD continues to monitor water quality in the region and share this data with research partners and the community which is essential to document long-term beneficial water quality improvements.
Requesting Data
Additional data can be requested through MMSD Records Department via email at recordsrequest@mmsd.com , “Contact us” form on mmsd.com , or in person during regular business hours.
Data are uploaded annually to USEPA’s data warehouse and can be viewed or downloaded on the National Water Quality Monitoring Council Water Quality Portal ( https://www.waterqualitydata.us ).
