We examined the use of pressure-sensitive film (PSF) to estimate pressures experienced by fish exposed to potentially damaging mechanical and fluid structures during downstream passage at hydroelectric dams. The films responded well to a wide range of applied pressures (0.5–50 MPa), providing reliable estimates of pressures even when contained within waterproof plastic packaging, stacked under other films, and exposed at low water temperatures or low and high relative humidities. Waterproof packages of PSF were field-tested by wrapping them around polycarbonate plastic cylinders and passing them down the spillways of hydroelectric dams. Most of the spillway-passed PSF samples had marks indicating impacts. Many of the marks revealed high values of pressure (e.g., >40 MPa) that are likely to injure fish.