The State of New Mexico and the Pueblo of Isleta have established surface-water standards for trace elements to control discharges of these contaminants. Before these standards can be meaningfully applied, however, ambient concentrations and loads of trace elements, principally arsenic, need to be determined in the Rio Grande and inflow sources. Arsenic concentrations also need to be determined in the edible portion of fish tissue because the Pueblo of Isleta standard for arsenic is based on fish consumption. Eighteen surface-water sampling sites on a reach of the Rio Grande from the Pueblo of San Felipe to Los Lunas, New Mexico, were sampled quarterly from October 1994 to August 1996. The sites include eight Rio Grande sites, one Jemez River site, five riverside drain sites, and four wastewater- treatment plant outfalls. Trace-element protocol was used to collect and process the samples. Field and laboratory quality-control samples were analyzed, and the results are included in this report. Fish-tissue samples were collected from four of the Rio Grande sites and the Albuquerque Riverside Drain, the Atrisco Riverside Drain, and three lakes at a recreational fishing area on the Isleta Indian Reservation. Arsenic in the Rio Grande is nearly all in the dissolved phase. There was little temporal change in arsenic concentration at the Rio Grande sites. The mean dissolved-arsenic concentration in the Rio Grande increased downstream from 1.8 micrograms per liter at the Pueblo of San Felipe to 3.6 micrograms per liter at Los Lunas. Mean dissolved-arsenic concentrations in the riverside drains were slightly higher (2.8 to 4.5 micrograms per liter) than those in the Rio Grande and were higher still in the wastewater-treatment plant outfalls (7.9 to 16.2 micrograms per liter) and the Jemez River (18.2 micrograms per liter). The mean total-arsenic concentration in fish-tissue samples from the Rio Grande and Albuquerque Riverside Drain was 14.53 micrograms per kilogram.