When a freshwater mussel clams up, it may be time to close the intake pipes at the Minneapolis waterworks in Fridley.

"If we smell something that doesn't seem right, we hold our breaths," said George Kraynick, the city's water quality manager. "That's what they do."

Minneapolis water officials are in the pilot project stage of trying to use about a dozen of the 3-inch-long, light brown mussels as an early-warning system for potential contaminants in the Mississippi River, from which the city draws drinking water for itself and seven other cities.

The work was initially supported by a U.S. Environmental Protection Agency grant, and more recently by technical help from an EPA scientist. Minneapolis and Moline, Ill., are working with the EPA to see if the freshwater muckets can serve as a warning system for the roughly 20 cities that draw water from the upper Mississippi.

"The [mussel's] bivalves are very sensitive to any kind of change in their environment," Kraynick said.

Normally, they draw water through a slight gap between their shells. That's how they filter nutrients from the water. But they're sensitive enough that a contaminant will cause them to clamp down. It could be a heavy metal such as copper or cadmium, an herbicide such as atrazine, or an industrial solvent such as toluene.

"You may not know exactly what you're concerned about," said Dave Hokanson, deputy director of the Upper Mississippi River Basin Association, a five-state group that has supported early warning research.

The importance of detection systems was highlighted last year when a toxic chemical that leaked into the Elk River in West Virginia contaminated the water supply for Charleston and 300,000 area residents.

Now that a memory chip on a computer that receives data from the monitors has been replaced, the Minneapolis biomonitoring system is operational.

Normally, water plant operators monitor incoming water for organic material that's washed into the river by rain or snowmelt. Their perceptions of smell lead to changes in how much powdered coal is added to the treatment to bind up the micro-contaminants and settle out of the water stream.

But the human nose is not as sensitive to minute amounts of other contaminants as are mussels. They're also quicker to give results than lab tests.

Still, mussels aren't without challenges. They need flowing water to thrive. Their tanks also need cleaning. They periodically also close on their own. That means each mussel's habits must be analyzed so that those operating the plant know what's a normal variation in a mussel's gap, and what's an outlier that could signal trouble. EPA scientist Joel Allen has been working on an algorithm that determines when a critical mass of mussels are reacting to a contaminant. When that happens, Kraynick said, the warning can be relayed by text message to plant operators.

Eventually, he hopes, the system can generate an audible text message for plant operators if the mussels detect a contaminant. If that happens, the city's reservoirs contain enough water to keep customers supplied for three or four days in the winter, and two in the summer — and water use restrictions could lengthen that.

Steve Brandt • 612-673-4438

Twitter: @brandtstrib