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Understanding Lake Health: The TSI IndexThe Trophic State Index (TSI) is a simple but powerful way scientists describe the health and productivity of a lake. It focuses on how much biological growth — especially algae — a lake supports, which is largely driven by nutrient levels. The index uses measurements like water clarity (often taken with a Secchi disk), chlorophyll-a (a pigment that indicates the amount of algae), and total phosphorus (a key nutrient). Together, these factors produce a score that shows whether a lake is clear and low in nutrients or nutrient-rich and algae-heavy.
TSI scores are grouped into trophic states. Oligotrophic lakes have low TSI values, meaning clear water, low nutrients, and little algae; these lakes are often deep and support cold-water fish. Mesotrophic lakes have moderate nutrients and productivity, with a balanced ecosystems supporting warm water fish. Eutrophic lakes have higher nutrient levels, more algae, and lower clarity, which can lead to low oxygen for fish. At the high end, hypereutrophic lakes are very nutrient-rich, often experiencing dense algal blooms and poor clarity. TSI levels can also signal nutrient pollution from runoff or development, making TSI a valuable tool for lake monitoring and management. |
2025 Water Quality Report
According to the 2025 Water Quality Summary Report prepared by Progressive Companies for the Marble–Coldwater Chain of Lakes Improvement Board, from 2016 through 2024, most lakes showed gradual signs of increasing productivity (higher TSI). In 2025, however, several lakes showed temporary improvement coinciding with a significant drought year that likely reduced watershed runoff and external nutrient loading.
This does not necessarily mean long-term pressures have disappeared. Rather, 2025 illustrates how strongly hydrology can influence lake response. Drought years can temporarily “reset” nutrient inputs, while wetter years may accelerate loading. For example, Coldwater Lake has returned to an oligotrophic state. The reported Trophic State Index (TSI) is the average of three parameters: spring mean total phosphorus, summer Secchi transparency, and summer chlorophyll-a concentration. While summer Secchi transparency fell slightly within the eutrophic range, this represents a notable and concerning departure from expected oligotrophic conditions that warrants close attention. Chlorophyll-a levels were very low and indicative of oligotrophic conditions. Spring total phosphorus also reflected an oligotrophic state, resulting in an overall TSI of 31.
These measurements are collected over the deepest basin of each of the lakes and may not represent conditions in nearshore, windswept areas where algae can accumulate, as some shoreline residents observed. Reduced water clarity is often driven by suspended sediments from heavy summer boat traffic. Read the 2025 Water Quality Summary here.
This does not necessarily mean long-term pressures have disappeared. Rather, 2025 illustrates how strongly hydrology can influence lake response. Drought years can temporarily “reset” nutrient inputs, while wetter years may accelerate loading. For example, Coldwater Lake has returned to an oligotrophic state. The reported Trophic State Index (TSI) is the average of three parameters: spring mean total phosphorus, summer Secchi transparency, and summer chlorophyll-a concentration. While summer Secchi transparency fell slightly within the eutrophic range, this represents a notable and concerning departure from expected oligotrophic conditions that warrants close attention. Chlorophyll-a levels were very low and indicative of oligotrophic conditions. Spring total phosphorus also reflected an oligotrophic state, resulting in an overall TSI of 31.
These measurements are collected over the deepest basin of each of the lakes and may not represent conditions in nearshore, windswept areas where algae can accumulate, as some shoreline residents observed. Reduced water clarity is often driven by suspended sediments from heavy summer boat traffic. Read the 2025 Water Quality Summary here.
Michigan's Cooperative Lakes Monitoring Program
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Monitoring Fact Sheets
Secchi Disk Transparency Dissolved Oxygen and Temperature Total Phosphorous Chlorophyll Exotic Aquatic Plant Watch Score the Shore 
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The Marble-Coldwater Clean Water Partnership Initiative was created to protect the Marble-Coldwater Chain of Lakes, building on the earlier volunteer-led “Keep Coldwater Clear” effort.
Since 2025, volunteers have monitored Coldwater Lake through Michigan’s Cooperative Lakes Monitoring Program (CLMP), initially collecting data on water clarity (Secchi disk) and invasive exotic aquatic plants to help detect potential issues early. Starting in 2026, monitoring will expand to all lakes in the chain and include temperature profiles, dissolved oxygen levels, water chemistry (phosphorus and chlorophyll), water color and appearance. Data will be collected multiple times each year to provide a more complete picture of lake health. All data will be analyzed annually to track trends and guide lake management, complementing ongoing monitoring by Progressive Companies, which has collected data since 2012 and manages invasive aquatic plants on the chain. Future plans include shoreline assessments through the CLMP “Score the Shore” program and continued volunteer involvement to support long-term lake health. To learn more about the parameters being monitored, take a look at the fact sheets listed here. If you would like to become a monitoring volunteer, register as an assistant volunteer on the MICorps Cooperative Lakes Monitoring Program (CLMP) website and sign up on the monitoring schedule on the volunteer page. |
Plant Control Data
A nuisance aquatic plant control program has been in place on the Marble–Coldwater Lake Chain since 2014. The primary objective of the program is to prevent the spread of invasive aquatic plants while preserving beneficial native species.
This program is commissioned by the Marble–Coldwater Chain Improvement Board and should not be confused with the Marble–Coldwater Clean Water Partnership (MCCWP). The Improvement Board is a Part 309 Board established under the Natural Resources and Environmental Protection Act, Public Act 451 of 1994. It is composed of the Township Supervisors of Quincy, Algansee, Ovid, and Kinderhook Townships, a Branch County Commissioner, the Branch County Drain Commissioner, and one at-large riparian representative.
The MCCWP is working closely with the Improvement Board in the development of the Watershed Management Plan (WMP). The goal of the WMP is to reduce nutrient inputs to the watershed, which in turn will help reduce the need for chemical use in aquatic plant management over time.
As part of the watershed planning process, the MCCWP is also reviewing the feasibility of a broader integrated aquatic vegetation management approach to reduce chemical use. This includes evaluating complementary tools such as benthic barriers and diver-assisted suction harvesting, along with other targeted non-chemical strategies, mechanical harvesting, and continued chemical treatment where necessary. The focus is on identifying a balanced, long-term approach to lake management.
No recommendations regarding changes to the current management approach will be made until the Watershed Management Plan is complete and all relevant data has been collected and reviewed.
However, the Marble–Coldwater Chain Improvement Board remains the entity ultimately responsible for the aquatic plant management program and retains full decision-making authority over any program changes. Any proposed modifications would follow the Board’s established process, including required public hearings, and would be subject to final approval by the Board. Consideration of program changes also includes evaluation of cost implications and public input.
In addition, through volunteer participation in the MICorps Exotic Aquatic Invasive Plant Watch Program, newly infested areas can be identified early. This early detection effort strengthens ongoing management activities and helps prevent future infestations from becoming established.
The following map displays treatment areas and products used for the 2023, 2024, and 2025 treatment seasons. The current program is funded through a special assessment district.
This program is commissioned by the Marble–Coldwater Chain Improvement Board and should not be confused with the Marble–Coldwater Clean Water Partnership (MCCWP). The Improvement Board is a Part 309 Board established under the Natural Resources and Environmental Protection Act, Public Act 451 of 1994. It is composed of the Township Supervisors of Quincy, Algansee, Ovid, and Kinderhook Townships, a Branch County Commissioner, the Branch County Drain Commissioner, and one at-large riparian representative.
The MCCWP is working closely with the Improvement Board in the development of the Watershed Management Plan (WMP). The goal of the WMP is to reduce nutrient inputs to the watershed, which in turn will help reduce the need for chemical use in aquatic plant management over time.
As part of the watershed planning process, the MCCWP is also reviewing the feasibility of a broader integrated aquatic vegetation management approach to reduce chemical use. This includes evaluating complementary tools such as benthic barriers and diver-assisted suction harvesting, along with other targeted non-chemical strategies, mechanical harvesting, and continued chemical treatment where necessary. The focus is on identifying a balanced, long-term approach to lake management.
No recommendations regarding changes to the current management approach will be made until the Watershed Management Plan is complete and all relevant data has been collected and reviewed.
However, the Marble–Coldwater Chain Improvement Board remains the entity ultimately responsible for the aquatic plant management program and retains full decision-making authority over any program changes. Any proposed modifications would follow the Board’s established process, including required public hearings, and would be subject to final approval by the Board. Consideration of program changes also includes evaluation of cost implications and public input.
In addition, through volunteer participation in the MICorps Exotic Aquatic Invasive Plant Watch Program, newly infested areas can be identified early. This early detection effort strengthens ongoing management activities and helps prevent future infestations from becoming established.
The following map displays treatment areas and products used for the 2023, 2024, and 2025 treatment seasons. The current program is funded through a special assessment district.
All Eyes On The Water Data
This map displays locations where observations have been reported through the All Eyes On the Water program.
Click any marker to view details about that report.
To learn more about the program, how to recognize invasive plants, invasive aquatic animals, harmful algal blooms, and foam — or to submit your own observation — visit the All Eyes On the Water page.
Click any marker to view details about that report.
To learn more about the program, how to recognize invasive plants, invasive aquatic animals, harmful algal blooms, and foam — or to submit your own observation — visit the All Eyes On the Water page.
Survey Participation Across the Chain
This map highlights properties around the Chain of Lakes where residents have already completed the community watershed survey. The survey remains open through July 31, and responses are still being collected. This map is intended to show participation across the watershed and encourage neighbors in areas not yet represented to take part. Survey results will be shared after the deadline.
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