The quality of surface and groundwater has been affected by abandoned strip mines and by abandoned underground mines in a 110-sq mi subbasin of the East Fork Little Chariton River. More than 14% of the area was strip mined for coal before 1979. The hydrologic system in the area was investigated and the effects of coal mining on quality of water in the river and alluvial aquifer were analyzed, with major emphasis on defining strip-mining effects. The groundwater gradient was from glacial drift or coal spring to alluvium to the East Fork Little Chariton River, and was greatest in spring and least in fall. Seepage from alluvium to the East Fork Little Chariton River occurs throughout the year, except during drought conditions when the only river flow is water released from Long Branch Lake. In the East Fork Little Chariton River median dissolved-solids concentrations increased from 153 mg/L near Macon to 630 mg/L near Huntsville and median sulfate concentrations increased from 36 mg/L near Macon to 360 mg/L near Huntsville. The median dissolved-solids concentration in water from the alluvium increased from 408 mg/L upstream from the strip mines to 641 mg/L near the mines and median dissolved-sulfate concentration increased from 140 to 350 mg/L. The sulfate-to-chloride ratio, used as the most sensitive indicator of strip-mining effects, increased markedly downstream in the East Fork Little Chariton River and nearby Middle Fork Little Chariton River, which also is affected by strip mining. There were no significant increases in sulfate-to-chloride ratio and dissolved-solids concentrations in comparable nearby subbasins of the Grand, Thompson, and Chariton Rivers where there was no mining. (Author 's abstract)