It is difficult to tell if there is an undertow just by looking. The slope of the shoreline affects the way the water flows. A gradually sloping shore will allow the water to flow gradually back out to sea. On a steeply sloping shore the water will flow very quickly, causing a strong undertow or backwash. Sandbars Sandbars are large areas of sand a short distance out to sea that are formed by the actions of the waves on the bottom of the ocean.
Sandbars also affect the outward flow of water.
By acting as a barrier, or dam, they force the water coming into the beach to find another way out to sea. The water runs along the beach forming a channel between the sandbar and the shore, causing a side current. Side currents flowing towards each other create rips.