In site processes for advanced fossil fuel recovery elicit major concerns about contamination of surface and groundwater with potential effects on water uses and aquatic biota. Acute and limited chronic toxicity bioassays were conducted to determine the effects process waters produced from in technologies being developed by DOE's Laramie Energy Technology Center Omega-9 retort water from the Rock Springs Site 9 in situ oil shale processing experiment and (2) hade condensate water from the Hanna underground equal classification experiment. The acute dilution toxicity level for oil shale retort water was about 0.5% for rainbow trout and fathead minnows and for dolphins (48 h) and the threshold effect dilutions for limited with rainbow trout.