Lakes and reservoirs in agricultural watersheds are often turbid with suspended sediments. The interactions among suspended sediments, dissolved organic matter, bacteria, algae and zooplankton will continually modify water quality. Our object was to evaluate the effects of dissolved organic matter (DOM) source, bacteria, and suspended sediments on the survival and growth in body length ofDaphnia pulex. We grewDaphnia in vitrowith different DOM sources (bur oak and hackberry leaf leachate), with and without suspended sediments. Daphnids grown in hackberry leaf leachate, with or without sediments, grew more than those in the corresponding bur oak leaf leachate treatments (P < 0.01). Bacterial density also was higher in the hackberry treatments compared to the bur oak treatments. Daphnids grew more in treatments with DOM plus suspended sediments than in the corresponding treatments without suspended sediments (P < 0.01), although bacterial density was lower in treatments with suspended sediments. Suspensions without daphnids had lower bacterial densities than those with daphnids. This experiment reveals some of the complexity of the interactions among the sediments, DOM, bacteria, and zooplankton that influence water quality. The results may have some applications to lake and reservoir management, particularly the biomanipulation of water and wastewater.