There are four tides per 24-hour period, two low tides alternating with two high tides, each approximately six hours apart. The typical difference between high and low tide in water depth at a given point is approximately seven feet (7 ft).  This means that at low tide, beaches are significantly wider (better for shelling) while rivers are significantly narrower and shallower.  River fishing is generally thought to be at its best several hours immediately before and after the crest (high point) or ebb (low point) of a tide.  Also, tides normally run higher in the Spring and Fall and at times of a full moon.