A detection system and method for a marine vessel uses an infrared sensor to detect the presence of a human being or mammal in a target area near the propulsor. A visible light detector is used to determine whether or not a signal received from the infrared sensor is caused by reflected sunlight and not the actual presence of a human being or mammal. By detecting visible light, false triggering of the system in response to infrared radiation received from sunlight can be significantly reduced. Embodiments of the system can monitor gear position and engine speed in combination with signals received from the infrared sensor and visible light sensors to determine an appropriate action to take in response to the presence of infrared radiation above a preselected threshold.