Indirect effects on macroinvertebrates or fish may be more appropriate for identifying regulatory thresholds for nutrients than direct effects on periphyton.  A way to approach these direct and indirect effects is through structural equation modeling, which characterizes relationships among several variables along model pathways leading to indirect effects.  Using data including measurements of nutrients, canopy cover, periphyton, macroinvertebrates, and fish from tributaries of the Little Miami River, Ohio, we tested a series of three tier models.  The variables in the first tier were total N, total P, N/P ratio, and % open canopy.  The variables were AFDM of periphyton, chlorophyll a, and % abundance, cyanobacteria + Chlorophyta in the second tier and a selected macroinvertebrate or fish metric in the third tier.  Metrics in the strongest models (indicated by low values for χ²) included % abundance, sprawlers, intolerant taxa richness, and % abundance, Trichoptera (macroinvertebrates) and catch per unit effort less tolerants and % abundance, darters & sculpins (fish).  In the models’ second tier, chlorophyll a and % abundance, cyanobacteria + Chlorophyta were important variables.  In turn, chlorophyll a was influenced by total N and % open canopy, while % abundance, cyanobacteria + Chlorophyta was influenced by total P.