Is a form of taxis seen in many aquatic organisms, e.g., fish, whereby they will (generally) turn to face into an oncoming current.
In a flowing stream, this behavior leads them to hold position in a stream rather than being swept downstream by the current.
In fish that exhibit rheotaxis, it can easily be demonstrated by creating an artificial current within a tank using pumps. No matter which way the pumps force the current to flow, the fish will immediately turn to face the oncoming current.