While sampling for aquatic life in a section of the Des Plaines River in southern Lake County last summer, ecologists knew they had snared something special in a fine mesh net.
But because the creatures were small -- about an inch long -- and translucent, they didn't recognize what they had found or that it would be a first in Lake County and a rarity in northeastern Illinois.
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Two of the see-through crustaceans taken as samples at the time were officially identified and documented last week as palaimonetes kadikensis, or Mississippi grass shrimp, one of two species of freshwater shrimp found in Illinois. The other, commonly known as the Ohio shrimp, has been found in the Mississippi River in southern Illinois.
Jim Anderson, natural resource manager for the Lake County Forest Preserve District, said he didn't need high-powered magnification to recognize a possible indicator of an improving aquatic environment.
"I knew what they were right away when I saw them, but we had to key it down to the species," he said of the close-up inspection.
Also known as glass shrimp because of their clarity, these creatures have been documented in only two other locations in Illinois -- Otter Creek near St. Charles and at various points along the Kankakee River, which joins with the Des Plaines to form the Illinois River.
Forest preserve ecologists netted about two dozen glass shrimp last summer, but the exact location isn't being divulged so collectors won't converge, Anderson said.
Unofficially, summer camp staff member Simon Helgeson retrieved what appears to be glass shrimp from the same stretch of the river in 2008. But he didn't realize what he had found, according to the district, and it was not officially documented.
How glass shrimp got to Lake County, how long they've been there or how many more there might be are unknown.
It could be that past surveys just weren't in the right spot.
"It is native and it does extend further north than this," according to Bob Rung, a stream biologist with the Illinois Department of Natural Resources. Rung said the species is fairly common but it "disappears pretty much" in the Chicago area.
"I've collected them in Alabama, Georgia, southern Illinois and locally. The Kankakee River has as large of a population I've seen anywhere," he said.
The junction of the Des Plaines and Kankakee rivers provides a possible route for the glass shrimp to head north, he said.
"There's probably of source of them that have been coming in slowly," Rung said. But he estimated the overall population in Lake County was very small.
Glass shrimp feed on algae, vegetation and other organic manner. Their presence indicates a good habitat of aquatic vegetation and possibly water quality.
"Essentially, shrimp are an indication things are in good shape in the stream," Anderson said. "The quality is getting better. I would say we have a lot more work to do, but this is a good sign."
Anderson and Rung presume glass shrimp are edible. But don't break out the cocktail sauce or plan a shrimp boil.
"They're just plain too small," Rung said.