Besides physical measurements such as water testing for chemicals or clarity, biologists often use inventories of “indicator species” to determine the ecological health of an aquatic ecosystem. Two groups of living organisms, fish and freshwater mussels, are excellent indicators of the overall ecological health of a stream or lake. The old adage “fish don’t lie” reminds us that water-dependent aquatic species cannot easily escape the impacts humans may have on their habitats.


While most people are familiar with “catchable” game fish species such as bass, bluegill, crappie, and catfish, these species tell only part of the water quality story. Many lesser known fish species that easily go unnoticed are more helpful to biologists assessing the quality of local water bodies. These fish include forage species that feed the more familiar game fish, as well as other species that are adapted to very specific habitats within streams and lakes. Some, like the darters, can be found in swift moving rocky riffles. Others, like top minnows, make their home among rich aquatic plant beds. Still others, like the stonerollers, live among the glacial cobble and rock that make up the bottom of many of our local lakes and rivers. Our waterways and lakes are home to these unique fish species, among many others:

pictures of freshwater fish

Freshwater Mussels

The diversity of fresh water mussel species found in streams and lakes, too, can be used by aquatic biologists to help determine overall ecosystem health. These silent storytellers, by their mere presence or absence, relate the tale of how degraded a water body has become. We now know, too, that there is a complex symbiotic relationship of mussel species with particular fish species that is essential to the reproductive success of the mussels; many fish species serve as physical hosts to young mussels for the first few months of their lives. Without the right fish species to interact with, a stream can gradually lose mussel diversity. The bi-state region has some of the best remaining streams and lakes in northeastern Illinois and southeastern Wisconsin, and the fish and mussels found here provide evidence of our good water quality, a resource to be proud of and protect. A few of the unique mussels found in our waterways include:freshwater mussels

Friends of Hackmatack enjoyed a virtual Annual Meeting in 2021, with the topic of “Saving North America’s Most Endangered Organisms – Freshwater Mussels. See our Videos & Virtual Meetings page for this and other presentation.

Click HERE to go directly to the video, featuring guest speakers Laura Barghusen, Aquatic Ecologist at Openlands, Kentaro Inoue, Evolutionary & Conservation Biologist from Shedd Aquarium, and Cindi Jablonski, McHenry County Conservation District Wildlife Ecologist.