Once you enter the water, determine if there is a surface current by observing a stationary reference point. Upon descent, observe the protruding sea life such as seafans, gorgonians, and rope sponges or schooling fish to determine which way the current is moving, or if there is a surge forcing these objects back and forth. Schooling fish will head into the current or duck behind an outcropping to be sheltered from it. Once you’ve determined the direction of the flow, swim against it for the first half of your dive—unless, of course, this is a drift dive and the boat is going to follow you. By swimming against the flow initially, you can drift back to your starting point at the boat when you’ve used half your air without risking undue fatigue or excessive air consumption.
As you continue through your dive, check on the current by stopping and drifting to check the velocity and direction. It is rare for the current to remain consistent in force and direction for an entire dive unless you stay in a small area. Generally currents will follow the bottom contour, but can change dramatically at walls, pinnacles, and underwater shelfs.
Downwellings & Upwellings are vertical currents especially prevalent along steep walls, as in Cozumel and Palau. This force can quickly take you deeper or shallower although you may have little sensation of moving. Be alert when diving in this terrain; as the ocean current meets a vertical wall it has to go up or down, as well as sideways. When currents flow from a shallow area over the top of a wall, it may flow downward, or out and eddy back, causing an upward current at the wall face. Either situation can sweep you many feet up or down without immediate realization unless you’re alert and keeping close track of your depth. Remember that 2 mph is 176 feet per minute.
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