A depth guide system gives an operator of a watercraft carrier an alert that the carrier is at a proper water depth to launch or stow the watercraft. The system includes an activator device or sensor having a housing vertically adjustable along a length of a vertical member. The device activates and deactivates the alert based on water level within the housing. When water is absent from the housing, the device activates a first LED at the top of the vertical member. When water located within the housing is sufficient to electrically connect two contacts, the device deactivates the first LED and activates a second LED of a different color at the top of the vertical member and can also activate an audible alert. A proximity sensor can be included which warns of any obstructions around the perimeter of the watercraft carrier via a secondary audible alarm.