Diamond Lake is located in southwest lower Michigan, in nearly the center of Cass County. It is situated southeast of the village, and county seat, Cassopolis. Four different townships intersect in its waters; Calvin, Jefferson, LaGrange, and Penn. The lake is 1,078 acres in size, 60% of the lake is less than 10 feet deep, and is 64 feet at its deepest. Most of its shoreline is lined with over 900 homes and cottages, including an occupied island of about 43 acres in the center of the lake, accessible to island residents by the privately owned barge/ferry during the summer months. There is one marina on its shores, and one public boat launch.

Water Quality


Michigan Clean Water Corps maintains a database of the results for the water samples and information collected by the Lake Preservation Committee for Diamond Lake data going back to 2003. This link will bring you to a search page, in the Raw data search section choose “LAKE”, then choose Diamond in the scroll box on the right of “Lake”. Scroll to the end of the page and choose to view in a webpage or as an Excel spreadsheet.

This link will take you to the Diamond Lake Guidebook recently published by Progressive A&E with assistance from the Diamond Lake Association.  It contains a brief history, information about the lake structure, and recommendations on how we can keep our lake healthy.


The Lake Preservation Committee of the Diamond Lake Association has taken an aggressive stance in monitoring and protecting our waters since 1992, the same year the sewer project was completed on our lake. A gradual improvement in water quality has been observed since that time. Diamond Lake residents are fortunate to live on a beautiful lake with high water quality and be a step ahead of the invasive weed issues that have plagued other lakes in the Great Lakes Region.

Maintaining Diamond Lake water quality is a collective effort, starting with citizen volunteers for the Collective Lakes Monitoring Program (CLMP).  The Diamond Lake water testing is currently conducted by volunteers:  Bob Clark (Chairperson), Fred Dean and Gary Gries.  The lake is tested weekly throughout the spring and summer for total chlorophyll a, total phosphorus and water clarity. Tests have also been taken for dissolved oxygen, e-coli and algae at various times. The  Water Quality report from the CLMP states that Diamond Lake, according to Carlson’s Trophic State Index, is a high quality Mesotrophic lake.

Additionally, invasive exotic weed invasion like Eurasian watermilfoil and Hydrilla verticillata require monitoring and treatment as necessary. The Diamond Lake Association has been treating Eurasian watermilfoil now for more than 5 years and growth has been substantially reduced.

Hydrilla is a robust aquatic plant not yet discovered in Michigan waters, but is thriving in similar lakes and streams in neighboring states. Hydrilla has many adaptive qualities that allow it to overpower and diminish or even eradicate native species. Hydrilla can grow up to an inch per day and disrupt the ecological balance of the lake. We cannot stop these invasive weeds from invading Diamond Lake but our goal is to stay ahead of the curve through constant monitoring, treatment, and preventative measures with non-resident boaters using our lake for fishing and recreation.

If you would like more specific information on water quality including copies of reports filed with the DEQ please contact Fred Dean at 269-445-2194 (Lake Preservation Committee Chairperson) or Bob Clark at 574-303-9552.

Download the June 2015 Weed Treatment Map


Gov't Info


Office of Sheriff
Sheriff Joseph M. Underwood
DIAL 911 for emergency
(269) 445-8644 non-emergency
Cass County Government Units Information — http://www.casscountymi.org
Cass County Road Commission — http://casscoroad.com
Cass County Telephone numbers
Other Cass area numbers
Cass District Library : (269) 445-3400
County Animal Shelter : (269) 445-3701
County Road Commission : (269) 445-8611
County Public Health Department : (269) 445-5280
Michigan Secretary of State, 601C North Front Street, Dowagiac : (269) 782-6512
Department of Public Works : (269) 445-4420