These data provide beryllium-7 (7Be) and excess lead-210 (210Pbxs) activity for fine-grained, mobile, streambed sediment in the Black Creek, Indiana (IN) stream-channel network. This basin is monitored in cooperation with the Great Lakes Restoration Initiative (GLRI). During the period July 22-25, 2019 (summer low flow), the thickness and spatial extent of soft, mobile, fine-grained (mainly silt and clay) streambed sediment was inventoried and sampled along 150-meter (m) transects. A combination of stream corridor land-use distribution, valley type, channel slope, stream order (Strahler, 1957), and ecoregion (Omernik and Griffith, 2014) was used to select 30 rapid geomorphic assessment reaches using methods of Fitzpatrick and others (2016); twelve of these were sampled for sediment fingerprinting and fallout-radionuclide (FRN) analysis.