All reaches of the Cedar River system above Cedar Rapids and down to its junction with the Ohio River possess the necessary nutrients and physical characteristics to support dense algal growths when climatological conditions permit. Rivers are dominated by phytoplankton that occupy streams in response to climatological factors. Under these conditions local actions are largely restricted to determination of densities attained in individual reaches. More critical nutrients for plant growth are supplied by surface wash of fertilized farmlands and sewage and other wastes discharged from cities. Tastes and odors developed in the Cedar River are attributed to excessive microorganisms in the water.