The toxicity of arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc to 2-mo-old rainbow trout in Whitewood Creek water was tested in continuous flow, 96 hr bioassays. Results showed test concentrations of arsenic ranged from 2.31 to 37.0 mg As/l. The 96-hr. TL50 for 2-mo. old rainbow trout was calculated to be 10.8 mg As/l. Cadmium concentrations in the bioassay ranged from 1.8 to 28.0 mg Cd/l. The TL50 was 6.6 mg Cd/l. Bioassay tests to determine the toxicity of chromium indicated the 96-hr. TL50 was 24.09 mg Cr/l. With the addition of Cr there was a drop in pH from 8.1-8.3 in the control to 4.6-5.0 in the 100 percent concentration. The 96-hr TL50 for nickel was found to be 35.5 mg Ni/l; for silver, 28.8 mg Ag/l; and zinc, 0.55 mg Zn/l. For copper , lead and mercury, the TL50 values were 253.0 ..mu..g, 8.0 mg and 33.0 ..mu..g respectively. Some or all of the metals tested may be more toxic than if heavy metals were absent from Whitewood Creek water. This study demonstrates the need for on-site bioassays. (CAJ)