The streams of southeastern Minnesota are very different from North Shore streams. Most rise from springs and thus are cool in summer. The limestone and alluvial soils in drainages make the streams hard, nonacidic, alkaline and very productive. Whereas the North Shore streams have relatively few aquatic insects, the southeast streams produce frequent hatches of mayflies, caddis flies and midges-all providing food for trout.
Nonetheless, southeast trout streams do have problems, most related to agriculture. Fence-to-fence grain farming on the uplands and pasturing of the river bottoms contribute to land erosion and sedimentation of the streambeds. This fine sediment covers the gravel runs and riffles that trout need to spawn and invertebrates need to survive. The clearing of shoreline trees takes away the underwater root wads and fallen trees in which trout find cover from current and predators. Finally, many of these streams simply aren't very large, and large trout find little cover. So, while the best of these streams may produce up to 300 pound of fish per acre-excellent production by any measure-18-inchers may be scarce except as figments of the imagination.
Because the chemistry and productivity of these streams are good, trout respond well to some kinds of habitat improvement. For example, the use of planks and boulders to build artificial overhanging banks increases big-fish cover, as does the placement of boulders in channel. Riprap prevents bank erosion. Wing dams and other current deflectors keep silt from key areas.
Brown trout are the trout best suited to the southeast streams. In the best of these rivers, such as Trout Run (in Winona and Fillmore counties), browns are self-sustaining. In other streams, such as the South Branch of the Whitewater, natural reproduction is augmented with stocking. In a few streams, spawning habitat is extremely limited, and the trout fishery is maintained entirely by stocking. Most people fishing these streams would regard a 14-inch brown as large, though some trout occasionally exceed eight pounds.
Some small southeast tributaries support wild brook trout; other streams are stocked with brookies. Some strains of rainbow trout have been tried in these creeks. Unfortunately, rainbows tend to migrate to larger, less suitable water so success with this species has been limited.