Sediment collected from the western basin of Lake Erie has a median particle size of 1.5 mu m and a median settling velocity of 0.0002 cm sec (super -1) measured by standard settling tube analysis. Microscopic examination of this sediment shows that most of the particles are bound into larger cylindrical aggregates by the feeding activities of tubificid oligochaetes (average pellet size = 280 mu m length x 70 mu m diameter). Standard settling tube analyses destroy oligochaete fecal pellets and maintain particles in an unnatural disaggregated state. Laboratory experiments and field observations indicate that for most of the year the top 0.5-1 cm of western basin sediment is pelletized. Less destructive settling velocity measurements of surface sediments yield median values of nearly equal 1 cm sec (super -1) for tubificid fecal pellets, 0.06 cm sec (super -1) for the top 1 cm of western basin sediment, and 0.03 cm seca for degraded fecal pellets. No realistic measurement of the physical properties of Lake Erie sediments, of sediment erosion and transport, or of diffusion rates of pore water solutes can be made without understanding the biological processes active in fine grained sediments.