This report describes a sportfishery planning model, RIOFISH, developed for use in large New Mexico reservoirs. RIOFISH is a comprehensive planning tool that simulates a fishery planning system including procedural input, the socioecosystem, and outputs pertaining to fishing opportunity and angler benefit. RIOFISH organizes information into simulations of reservoir inventories and can be used to forecast resource and angler response to management strategies applied in different possible planning environments. The model also may be used to facilitate decisions based on anticipated angler benefit and agency management costs. RIOFISH can be used to evaluate which parts of the planning system have the most impact on model outputs and require the greatest resource attention. RIOFISH simulates hydrologic, biologic and socioeconomic interactions in 16 large reservoir fisheries of the Rio Grande and the Canadian, Pecos and San Juan rivers. The model user can modify water levels; reservoir exchange rate; concentrations of nutrients, suspended matter, and organic matter; temperature; solar radiation; fish stocking rate and regulations; fish introduction, removals and mortality effects; and road and boat ramp access. Outputs include simulation of river and reservoir hydrology, water quality, organic loads, fish production and catchable sportfish, catch rates, recreational days, and angler benefits. RIOFISH is run reiteratively, with each subsequent model scenario contrasted with an initial reference run.