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Did You Know? Cook County is Home to 17 Species of Clams

the Des Plaines River at Columbia Woods
A view of the Des Plaines River from Columbia Woods.

The water bodies throughout Cook County benefit from unusual ecological diversity. From various species of aquatic plants to numerous species of fish and other wildlife, Cook County residents and visitors can spend leisurely days exploring the interesting world of our lakes, rivers and streams.

But did you know that included in this great biodiversity are more than 17 species of clams? Though they may be more commonly associated with coastal communities, Cook County is in fact home to these inconspicuous bottom dwellers.

Each year, the Forest Preserves of Cook County conducts clam surveys of the local rivers and streams. According to Senior Wildlife Biologist Chris Anchor, clams are one of the standards for understanding the quality of these water habitats, both of the bottom of the lake or stream as well as the water quality.

“Clams are pretty sedentary, so once they set up shop somewhere, they have a very small home range. They’re a good indicator of what is happening at that exact spot, whereas in most moving waters, obviously, the water is always moving,” explains Anchor. “Fish can die and be swept away or move away. And although they’re an excellent indicator, their absence may or may not tell you something. They can also move around, thus provide misleading information about any specific area.”

In the last three decades, Forest Preserves biologists have detected 17 different species, but typically only spot 13 to 14 different species any given year. Anchor explains this is because some species of clams are extremely conservative, only able to live in certain conditions. Additionally, two species are exotic to our area.

Though they may look identical, there are some differences between freshwater clams and their sea-loving counterparts.

“The biggest difference is that some of our freshwater clams are very long-lived, and can last 40 to 50 years. Whereas most sea-living clams live for about 10 years,” says Anchor.

While anglers may be tempted to collect these interesting aquatic animals, it is illegal in Cook County to harvest freshwater clams.