Water Quality

An indelible imprint: The MWRD’s legacy on area water quality is clear

Click here for MWRD's water quality data and reports. 


There are few priorities as critical to the MWRD as water quality. By its mission, the MWRD aims to protect the source of drinking water in Lake Michigan, just as it works daily to protect the Chicago Area Waterway System (CAWS) and treat and clean about 1.3 billion gallons of wastewater per day. The MWRD constructed local waterways more than 100 years ago for the purpose of reversing the flow of the river with the main intent of protecting the drinking water supply, providing drainage for the Chicago region and conveying wastewater. One look at the kayakers, water taxis and riverfront development and it’s clear that the Chicago River and surrounding waterways mean much more to the region in the 21st century. It has taken years of investment, testing and innovation from the MWRD to improve the conditions and quality of water there is today.



It all begins at the MWRD’s water reclamation plants (WRPs), where treatment plant operators, operating engineers, electrical operators, tradesmen and women and other Maintenance & Operations staff keep plants running and billions of gallons of water clean, using both tried and  true processes and innovative technologies to protect the water environment. But the efforts behind improving local water quality can also be found in MWRD labs, in the communities where MWRD environmental specialists and the MWRD Industrial Waste Division patrols, underground and surrounded by limestone where Tunnel and Reservoir Plan (TARP) engineers plan for ambitious projects to mitigate pollution and flooding, in the greenhouses where MWRD soil scientists recover valuable resources from the treatment process, and on the very waterways where MWRD crews remove debris from the water, aquatic biologists study fish and pollution control technicians pull water samples. When it comes to protecting the region’s water environment, all MWRD personnel’s hands are on deck.


The MWRD has been annually recognized for its work protecting the water environment and meeting stringent permit guidelines no matter what force of nature is thrown its way. The MWRD and its WRPs do not take days off. The water keeps flowing, and the MWRD takes immense pride in providing this critical service for 10 million people each day.



The initiatives the MWRD has taken in protecting area waterways has resulted in cleaner water and a surge in recreational activity and economic development. The demand for the new Chicago Riverwalk, Cal-Sag Trail, 312RiverRun, Centennial Trail, Ping Tom Park and new Chicago Park District boathouses and developments completed at Wolf Point and proposed for Lincoln Yards are not possible without cleaner water. These water quality improvements have proven to be essential factors for nurturing aquatic life and a healthy river system once unimaginable less than a century ago. The MWRD acknowledges  it cannot simply erase years of pollution in waterway sediment and uncontrolled wildlife activity, but the future has perhaps never been as bright as it is today for the local water environment. The MWRD has accomplished these water quality improvements through a variety of means.













TARP: Once completed in 2006, the tunnel portion of TARP cut the number of combined sewer overflow (CSO) events in half. In the Majewski and Thornton Reservoir service areas, the completion of those reservoirs has nearly eliminated CSOs and this form of pollution. Since the Thornton Composite Reservoir came into service in late 2015, there have been only been a handful of reported CSOs in the Calumet River System, and the Calumet TARP system has captured over 99 percent of the volume of CSO discharges since the reservoir was placed into service. The addition of McCook Reservoir is also improving water quality. Stage I of the McCook Reservoir is now in service. When completed, both stages of McCook Reservoir will have a total capacity of 10 billion gallons. TARP has contributed to measurable declines in wet weather concentrations of biochemical oxygen demand (BOD) and suspended solids, meaning improved dissolved oxygen (DO) levels in the water, resulting in healthier waterways.




Since disinfection came into service in 2016 at O’Brien WRP and Calumet WRP, the ambient monthly CAWS fecal coliform (FC) data demonstrate improvements following disinfection. Fecal coliform concentrations at monitoring stations directly downstream of WRPs have decreased substantially since disinfection. During recreation season between March and November, MWRD disinfects the treated water at the O’Brien and Calumet WRPs; staff collect and analyze daily disinfected water samples to evaluate and monitor the performance of the system.



The MWRD has also introduced sidestream elevated pool aeration (SEPA) stations and other instream aeration stations to help inject needed oxygen into the waterways. The SEPA stations might function as an attraction for scenic views, photo opportunities, park activities and picnics, but these waterfalls also work to enhance the water quality and create new life in the CAWS.

Nutrient Recovery


The MWRD has been proactive in addressing nutrients to improve local water quality and as a sustainability initiative even before required by regulation. Phosphorus enters the WRPs in the raw sewage and originates from several sources including human waste, animal waste, fertilizers, detergents, and cleaning agents. In the Chicago area, phosphorus is added into drinking water to control pipe corrosion and lead release, which can contribute as phosphate to the area’s wastewater. Collaborating with the environmental community and the Illinois Environmental Protection Agency, the MWRD is committed to meeting aggressive goals of reducing phosphorus by 2030, and is already meeting many of those goals at Stickney WRP, where 97 percent of total phosphorus was removed in 2018. Many of these improvements are credited to the MWRD’s new nutrient recovery system, which converts that phosphorus into a slow-release fertilizer to be reused to benefit the environment.

Phosphorus Assessment and Reduction Plan Fact Sheet

In June 2021, the MWRD began developing a Phosphorus Assessment and Reduction Plan to identify and address unnatural plant or algae growth that could be caused by excess phosphorus in the Chicago Area Waterways System (CAWS). The CAWS is the network of rivers and waterways extending through much of the Chicago metropolitan area. The Plan will serve as a roadmap for improving water quality in the CAWS, which will benefit the surrounding communities. This fact sheet provides an overview of this project.


Skimmer Boat


In 2015, the MWRD added skimmer boats to its fleet, providing more tools to respond to pollution and debris in waterways. In addition to the two skimmer boats, the “Skim Pickens” and “Skimmy Dipper,” the MWRD operates a 36-foot debris boat with a 25-foot by 50-foot barge for removing larger objects and two pontoon boats to collect floatable trash. The MWRD boats help protect the waterways by collecting nearly 200 yards of debris each year. These debris collection boats provide a vital community service by improving water quality and the recreational experience for thousands of people canoeing, kayaking, boating, and enjoying the waterways. In addition, the MWRD’s Small Stream Maintenance Program promotes clean water and reduces flooding in urbanized areas by removing downed trees or low hanging branches, dense weeds, invasive plants and addresses eroding stream banks.

Click here for amounts of debris collected from the river.  

Scientists with the MWRD and the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory are currently examining water quality through a groundbreaking seven-year study. The CAWS Microbiome Study examines the complex microbial communities in the CAWS using advanced analytical and computational tools to explore what microorganisms exist, where they came from and what they are doing. Like many other river systems, the communities vary in their makeup based on location and a variety of other factors, but are generally stable. The second phase of the study determined that the CAWS has more than 20,000 species of microbes in the water and sediment. The microbes are environmental bacteria that are present in water from homes and industries and in stormwater. The diverse microbial community found in the CAWS was determined to be healthy with a stable community of microorganisms, typically found in fresh water streams. The genetic analysis of these microbes has provided insight into the sources of the bacteria, ranging from fish and sediment to treated water and sewage.

Click here for more information. 

The MWRD collects monthly water samples at 28 locations throughout the agency’s 882-square-mile service area throughout Cook County. They then return these samples to the lab, where they analyze the water for dozens of chemical and biological constituents. The MWRD also operates continuous monitors, which collect hourly DO levels, specific conductance measurements, and temperature readings at 22 locations throughout the waterways in the MWRD service area.

The MWRD monitors water quality in Chicago area rivers and streams. Water quality data including fish populations, dissolved oxygen and water chemistry are available here. If you have any questions about MWRD's waterway monitoring programs or specific data requests, contact waterqualitydata@mwrd.org. 

Waterways Chart

The MWRD also conducts fish monitoring periodically throughout its service area, which includes the Chicago, Calumet, and Des Plaines River Systems. The number of fish species found in the Chicago Area Waterway System (CAWS) has drastically increased since the 1970s when monitoring of the fish population first began. From 10 known species in 1974, that number has ballooned to 77 by 2019, including 60 that have been found in the CAWS since 2000. Thanks in part to advancements at MWRD water treatment operations, the waterways have experienced decreases in levels of ammonia and BOD. The BOD captures the degree of pollution by measuring the amount of DO that must be present in water for microorganisms to break down organic matter in the water at a certain temperature over a time period.





The MWRD’s work does not rest with improving water quality. The MWRD is also improving access to the water, collaborating with municipalities and park districts to provide nominal leases for use of MWRD land for recreation, and forming partnerships with the U.S. Army Corps of Engineers, Chicago Park District, Friends of the Chicago River and the Metropolitan Planning Council to improve riverfront trails, restore riverbanks and remove dams, like on the North Branch of the Chicago River, to allow upstream fish migration and improve navigation and surroundings for boaters. Together, the Chicago area waterways have a brighter future—and cleaner tomorrow.

River Runner

Click here for a visualization that follows a drop of rain almost anywhere in the U.S.