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I I I I I I I I I I I I I I I I I I I the San Miguel River, again suggesting inputs in the Paradox Valley area. Values were similar between trips although the variance was high within trips. High levels of phosphate may lead to the development of plant nuisances within the flowing water and, in turn, development of animal pests that may become associated with such plants. Mackenthun (1973) set the desired goal for the prevention of plant nuisances at 0.1 mg/L for flowing waters not directly discharging into lakes or impoundments. There are no criteria for phosphate set by the EP A Ortho Phosphate Ortho Phosphate levels were consistently low, ranging from <.01 to 0.044 mg P04_p IL on trip #2. There were no discernable trends between study reaches. No EPA criteria have been established for ortho-phosphates. Metals On trips 1 and 2, copper, iron, lead, and zinc were measured as total concentrations; because of high levels of these metals detected, analysis for trip 3 was expanded to also include the measurement of dissolved concentrations. Maximum concentrations of total metals were 0.282, 32.8, 0.180, and 1.20 mg/L, respectively, for copper, iron, lead, and zinc, and <.01,3.42,0.080, and <.01 for the dissolved forms of the respective metals. In general, trip 1 showed lower total metal concentrations than were found on trips 2 and 3. In all cases, levels usually peaked. above the confluence at the San Miguel River. Concentrations of both copper and iron in the Dolores River as measured in 1990 were substantially higher than reported in 1960. Copper levels measured just above the San Miguel confluence in 1960 peaked at 0.010 mg/L (USPHS 1961), compared to a high of 0.282 near this location in 1990. Copper levels in the San Miguel River were similar in both studies (<0.2 mg/L). In 1960, iron measured 0.08 mg/L in the Dolores River just above the San Miguel confluence, compared with 27.0 mg/L for the same area in 1990. Less iron was detected in the San Miguel River in 1960 (0.08 mg/L) than in 1990 (4.45 mg/L). No historical information for lead and zinc could be found The toxicity of copper, as well as iron, lead, and zinc, is inversely proportional to water hardness (EP A 1986). Based on the range of water hardness in the Dolores River the EP A Criteria states that freshwater aquatic organisms should not be affected unacceptably if the I-hour average concentration does not exceed 0.024 - 0.142 mg/L total copper (again, depending on hardness) more than once every three years on the average. However, these values do not apply to situations where a locally important species is very sensitive. When 41 genera of freshwater species were tested for sensitivity to copper, Ptychocheilus was found to be most sensitive. Copper becomes acutely toxic to squawfish at concentrations of 0.016 mg/L at a hardness of 50 mg/L. Although high levels of water hardness temper its toxicity, copper may still be present in high enough levels to adversely affect native fish species, especially the squawfish. The EP A has set 1.0 mg/L as the maximum acceptable level of iron for freshwater aquatic life (EP A 1986). This value was exceeded in 10 out of the 13 water samples taken on the Dolores River in 1990. The highest concentration of iron was found on trip 3 above the confluence of the San Miguel River, and was over 32 times the maximum value set by the EP A for protection of freshwater aquatic life. Although specific criteria were set, EP A does not state possible adverse effects of unacceptable iron levels. 18