Contents of a typical postindustrial pond that was used 12 years previously as a tank for collecting waste water pumped from a coal mine was evaluated on the basis of 19 samples collected from the pond and surrounding area. Measurements of radium, thorium, and potassium, plus cesium activity, were performed with the use of a germanium detector – HPGe 4020 by examining photons with energy in the range 0.5 MeV to 3 MeV. In consequence, the concentrations of such radioisotopes as ²²⁶Ra, ²³²Th, ⁴⁰K and, ¹³⁷Cs were determined by their decay products, but the radiation effect of natural radioisotopes was estimated by I₁ and I₂ coefficients. The investigation shows the most contaminated residue in the sediments at the bottom of the settling tank.