The influence of municipal and agricultural practices on stream water quality in the Grand River Basin was examined in terms of the resulting phosphorus and nitrogen inputs to Lake Michigan. Phosphorus and nitrogen concentrations in the Grand River watershed indicated that nitrate-nitrogen fluctuated significantly with changes in temperature and photoperiod, while total phosphorus concentrations were not influenced by these indexes of biological activity. A study of nutrient concentrations in runoff from watersheds of predominantly urban, natural, or agricultural land usages indicated significant differences: The natural watershed runoff contained less nitrate-nitrogen than did runoff from either the urbanized or agricultural watersheds; Urbanized land runoff contained far greater concentrations of phosphorus than did runoff from either natural or agricultural watersheds; and Natural and agricultural land runoff did not contain significantly different concentrations of total phosphorus. General observations of nutrient fluctuations in the Grand River system indicated evidence of possible nitrogen-limitation during the period of surveillance. (Author)