Conservative no-effect concentration ranges were estimated for ventilatory and coughing responses of bluegill sunfish Lepomis macrochirus and brook trout Salvelinus fontinalis exposed to altered pH, or to changes in dissolved oxygen (DO), suspended solids, or dissolved solids concentrations. These limits predict safe, or non-alarm-causing, variations of these non-toxic environmental variables in applied biomonitoring systems using Lake Superior or similarly constituted waters as a dilution source.