Whether electrofishing juvenile fish in a stream to obtain population estimates or cleaning hatchery raceways, our activities can stress fish. As much as possible we try to avoid stressing fish as this can have negative effects on most biological processes, including disease resistance, growth and reproduction. We can measure the degree to which an environmental condition, human activity or other variables stress a fish by measuring the animal's stress hormone levels. In so doing, we may take actions to reduce the stressful conditions experienced by the organisms we manage.