The New Mexico based fishery planning model, RIOFISH, was modified and applied to Saguaro Lake (near Phoenix, Arizona) to evaluate the effects of several probable events on estimates of angling opportunity and economic benefit (consumer surplus) gained from adding artificial habitat to Saguaro Lake. We developed model senarios for Saguaro Lake based on assumptions that restricted parking lot size limits lake use and provision of artificial habitat will double fish catchability by concentrating fish near the new habitat. Five hypothetical but probable conditions were tested for no effect on the benefits generated by the artificial habitat including 1) variable water supply, 2) variable nutrient concentration, 3) increasing human population density, 4) decreased largemouth bass mortality, and 5) increased lake surface area in nearby Lake Pleasant. All five hypotheses were rejected — all five factors were influential. Parking lot size, low lake fertility and attractive fishing at substitute lakes (especially Lake Pleasant) caused lower than expected estimated economic benefit from artificial habitat placed in Saguaro Lake. Model results call into question estimates of benefit:cost that exclude consideration of important variables that influence the dynamics of the entire system of fishery sites from which anglers choose to fish.