Essentially, Mike Davis and the Minnesota River Watershed Alliance was inviting people to get up early on a Saturday morning and reach their hands into the muck in hopes of finding something slimy.

About 25 people of all ages gladly accepted the invitation.

“It’s very encouraging to me,” said Davis, a freshwater mussel expert for the Minnesota Department of Natural Resources. “... People are really awakening to the value of rivers as educational tools and recreational opportunities.”

The Watershed Alliance also hyped the event a bit, asking people to “Explore the Wonderful World of Mussels” through a classroom session by Davis Friday night and the hike in the Cottonwood River Saturday morning. He had plenty of interesting stuff to say about the seemingly not-so-interesting blob that kids have found when they’ve pried open a freshwater clam.

First off, some mussels will live a lot longer than most people.

“Many species we think can live to be over 100 years old,” Davis said.

And then there’s reproductive techniques. Let’s skip ahead to the part where fertilization has already occurred and the female mussel has a whole bunch of mussel larvae she’s looking to get out of the shell.

Often, the females will trick fish into giving the larvae a ride. Some species of mussels open their shell and wiggle a minnow-shaped piece of flesh until a predator fish mistakenly tries to take a bite out of the “minnow” and winds up with scads of mussel larvae attached to its gills.

Others can mimic insects to attract fish for the larvae-dump, doing what fly-fishermen do when they “match the hatch.”

“Mussels have been doing that for thousands of years,” Davis said.

Then there’s the snuffbox mussel that targets a certain type of perch — a perch that feeds by flipping over stones on the river bottom and eating what’s beneath. The mussel positions itself to look like a stone but captures the perch when the fish tries to flip it. For a half-hour or so, the perch is inside the shell where the mussel pumps larvae into its mouth and through its gills before releasing the fish.

“So treachery’s a lot older than humans,” Davis said.

But the world isn’t so wonderful for mussels living in rivers like the Cottonwood or the Minnesota. Contaminants in the water and the repeated and rapid rising and falling of river levels, caused by extensive farm-field drainage systems, have reduced mussel populations dramatically in the last century or so.

“There used to be 40 (species) in the Minnesota River,” he said. “Right now, there’s 15 to 20.”

Mussels have been compared to coal-mine canaries as they warn humans, through their deaths, that there’s trouble brewing. Mussels, however, also contribute to healthier rivers by absorbing bacteria and excess nutrients and by stabilizing river bottoms. Even the fish who get the larvae treatment appear to be granted a level of immunity to future parasites by carrying the larvae.