The Blue River of Southern Indiana, a fourth order tributary of the Ohio River, has the reputation of being a high quality, scenic stream with an ample population of game fishes. It is know for its endangered spotted darter (Etheostoma maculatum). The spotted darter originally inhabited the swift riffles of medium-sized rivers from Illinois to Pennsylvania to southern Tennessee. At the present time, they are difficult to find in most of the former range. Dr. Claude Baker et al. (1984) found the first verifiable spotted darter population located in Indiana this century at the Blue River. A unique aspect of the river is the large number of caves and springs that empty into the mainstream of the river. The largest spring in Indiana, Harrison Spring, and the largest cave in Indiana, Wyandotte Cave, are located on the watershed.
Physiographically, the Blue River is located in the Escarpment Section of the Shawnee Hills Natural Region. This rugged section of the hills situated along the eastern border of the region often blends with the well-know Mitchell Karst Plain of the Highland Rim Natural Region. The upper forks of the Blue River are located almost wholly in the Mitchell Karst Plain.
The headwaters of the stream are well to the northwest in Clark, Scott and Washington Counties in Indiana. In Washington County, various creeks and smaller branches combine to form the South, Middle and North Forks of the river. The Middle and North forks join south of Salem while the south fork flows southwest joining the Blue River just north of Fredricksburg, Indiana. Below Fredricksburg, the only tributary of any consequence, Whiskey Run, enters the stream north of Milltown.
The mainstream of the Blue River serves as the border between Harrison and Crawford Counties along the major portion of its 45-mile length. Years of erosional processes and cave formation have produced a watershed with sloping hillsides covered by several species of deciduous trees. Riparian vegetation includes large sycamores with characteristic root-wads providing habitat for centrarchids like rock-bass and long-ear sunfish. In some areas, the river has a sufficient floodplain to provide flat farm-land. The major soil along the river is the Haymond Silt Loam, a deep, nearly level, well-drained soil with a moderate amount of organic matter.
The river has a fairly typical set of in-stream features including alternating fast water riffles and slower moving pools. A distinguishing feature, however, is that some riffles are quite swift providing the preferred habitat for the endangered spotted, bluebreast and variegate darters. The banded darter is quite common in the swift, high discharge riffles, but it inhabits the slower riffles as well. Most riffle areas have boulder, cobble and gravel substrates that offer shelter and attachment areas for fishes and macroinvertebrates. Dissolved oxygen levels are near saturation in these riffles. Near the riffles, one often finds a gravel outwash community consisting of smartweed, small sycamores and water-willow growing in the rocks and sand. Mussel shells are often washed into these areas during flooding. Many pools in the Blue River are long and deep and also have a variety of shoreline fish habitats including root-wads, logs, brush and rock outcrops. Some areas with mud banks have undercuts that provide additional shelter for game fishes.
This area has four well-defined seasons with daily temperatures ranging from the low twenties in the winter to the high nineties in the summer. The weather is continental by nature and is variable because of its position in the mid-latitudes. The Blue River is in a belt where southwesterly winds bring storms when moisture is pumped up from the Gulf of Mexico ahead of fronts. As winter storms move from west to east, the area is subject to rainfall. During the spring and summer, point source thunderstorms and fronts can dump considerable precipitation that causes the river to rise dramatically. At these times, the river will run muddy for several days. The month with the lowest rainfall is usually October. During this month, the river often is low and clear. In 1999, drought conditions throughout the spring and summer months greatly affected the normal water depth of the river for those months. Rather than the high muddy conditions found in the Blue River during the spring and summer, the water was relatively low and clear. These uncommon low water conditions resulted in an extra accumulation of organic matter in most riffles.
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