Abstract: An illumination device for directing light into a transparent fluid tank of a fluid-resistance exercise machine is disclosed. The device can be coupled with an exterior surface of the tank and includes a light source oriented to project light through a surface and into a region of the fluid tank where the light can be observed by a user of the machine during operation, especially when a rotary device disturbs the fluid to generate the fluid resistance effect. The illumination device can include a control unit having a processor and a communication device, where the communication device receives an exercise-related parameter relayed during operation of the exercise machine. In response the control unit can dynamically adjust a quality of the light as a function of the received parameter, such as heartrate, output, resistance, time, distance, or speed.