EPA requires major municipal and industrial dischargers to conduct biomonitoring – whole effluent toxicity (WET) tests – on their effluent. Indicator species, typically water fleas and fathead minnows, are exposed to various dilutions of the entire effluent. Survival and, in some cases, growth or reproduction are observed and compared to a control group to indicate whether or not a discharge will have a toxic effect on the receiving stream. Failure of a toxicity test requires the permittee to perform additional analysis to determine the source(s) of the toxicity. The permittee must then reduce the toxic concentration(s) in the effluent. Reductions often come through upgrades to the treatment system or reducing the toxic concentrations before they get into the treatment system through a public education program. The latter is particularly effective for pesticides and herbicides.