The data is supplemental to the 2018 USGS Open File Report, "An evaluation of the acute and chronic toxicity of potassium chloride, active compound in the molluscicide potash, on salmonid fishes and their forage base". This research was performed as a Science Support Partnership (SSP) study with USFWS in order to evaluate potential lethal and sublethal impacts of potassium chloride on salmonid fishes and selected invertebrate forage. Files in this data set describe blood chemistry parameters, plasma osmolality and cortisol, gill chloride cell abundance, and fish total body weight and total length for specimens from each of the two salmonid species tested (brook trout, Salvelinus fontinalis, and Chinook salmon, Oncorhynchus tshawytscha). Files are include acute toxicity testing data for each of the three invertebrate groups (Chironomid larvae, Dapnia magna, and Procambarus sp. crayfish).