In 1996, the oligotrophic Neunzehnhain Reservoir (Erzgebirge Mountains, Ger
many) was completely drained. About 200 t of dry matter eroded from the sed
iments. Seepage of interstitial water caused high concentrations of dissolv
ed manganese in the outlet. Particles less than or equal to 0.2 mm intruded
into the hyporheic zone of the downstream brook. Tts macroinvertebrate com
munity changed significantly.