Having learned a great deal about these lampreys, I now find them to be some of our state's most interesting fish species. All of Minnesota's lampreys have similar life cycles. Adult lampreys ascend streams to spawn from late April to mid-June, depending on locale and species. Awaiting the onset of spawning, lampreys hide beneath rocks or other objects in fast riffles. I once found an American brook lamprey under a discarded oven door in the South Fork of the Zumbro River near Rochester.
Adults move out of riffles and just upstream to spawning areas in loose groups.
I've watched as many as a dozen lampreys move out of hiding within a few minutes and begin to spawn. What stimulates them to begin their spawning activities together remains a mystery. Although a single lamprey can construct a spawning nest, several lampreys often construct a nest together in beds of coarse sand, gravel, or cobble. To clear a spot for nesting, a lamprey picks up stones with its suction-cup mouth and laboriously pushes or drags them away. It also attaches its mouth to a rock and thrashes its body vigorously within the nest, stirring up sediment, which the current carries away.