Fish travel up and down this trough and look for food such as small fish, crabs and sandworms. On the Outer Banks, under normal conditions, we have approximately a two-foot difference in water depth along the ocean beach between low and high tides, and it's easier to locate a slough at low tide, when the sand bars are easily visible. When the water depth decreases suddenly in a short distance, such as in the case of a sandbar, the incoming waves will break on top of that bar. In the case of a gently sloping beach, with no outer bar, the waves will gradually spill over, and continue to do so until they eventually break onto the beach. This is what experienced surf fishers call a flat beach.
Beach sand can also be a tip-off about the contour of the ocean bottom.
Very fine, tightly packed sand is often found on a beach with a gradual slope. Coarse sand, or small gravel, is typically found on a steep sloping beach. Sometimes this coarse, large sand is often darker than the fine grain sand, and it's not unusual to find various types of sand over several miles of beach. The width of a slough may also be critical. On the Outer Banks, big fish such as red drum tend to prefer the wider, deeper sloughs, with some shallow, shoal water at either end.