In The Witch of Blackbird Pond, what is preventing the Dolphin from going up river? Describe "walking up the river".

In order to move, the Dolphin is dependent on the tides or the wind.  Since the journey from Saybrook to Wethersfield is upriver, or against the tide, the wind is the only natural force that can propel it forward.  The wind is capricious and unpredictable, however, and on Kit's first trip along this leg of the journey, "the fresh sea breeze drop(s) behind, and by sunset it (dies) away altogether".  As the sails sag "limp and soundless", there is little choice for the passengers and crew but to wait until the wind comes up again in the desired direction.  The crew is used to long delays in the area, but Kit is overcome with impatience.  On one or two occasions a "temporary breeze" raises hopes on the little ship, only to die away again after a short while.

Finally, after making little progress for seven days, the captain of the Dolphin resorts to an arduous process to get the ship moving.  The procedure is called "walking up the river", and relies on sheer manpower to pull the heavy boat, inch by inch.  Two sailors in a small boat row on ahead, carrying a long rope fastened to a small anchor.  They go as far as the rope will reach from the Dolphin, dropping anchor when it is stretched to its limit.  "Ten hearty men" then line up on the deck of the ship, each grasping the rope, and begin "a rhythmical march from one end of the ship to the other...as one man reach(es) the end, he drop(s) the rope, and race(s) back to grasp it again at the end of the line".  In this manner, the Dolphin is pulled, in almost imperceptible increments, forward through the water (Chapter 2).