We often need to fabricate specialized instruments for unique applications. In this case, we wanted underwater lights that operate on a timer to use with an existing Vaki Riverwatcher system owned by Seattle Public Utilities. We opted to use LEDs (light emitting diodes) because of their longevity and low power requirements. LEDs emit light without burning a filament, as in conventional lights, so they don’t burn out. The challenging part of the fabrication is sealing the ends of the light tube to ensure the light is waterproof. We tested these lights to be waterproof up to 10 feet deep, which should work well in the Landsburg Fish Ladder where the lights are going to be used. An advantage of custom making the underwater lights is that we can design them to operate on a conventional 120 volt AC power supply or on a 12 volt DC battery.