What is "undertows"

Usage examples of "undertows".

Even in winter, when the water was thick with suspended ice and sluggish with cold undertows, its current throbbed against the watch tower like a stallion's heart.

Usually green, except when riptides or extreme undertows were reported, it flew bright yellow, urging beachgoers to use caution in the water.

And so, with that challenge before us, let us try to become acquainted with some of the tides and undertows of our inward sea.

Under their feet was the ice, which was white also, and under that the river water, with its eddies and undertows, dark but unseen.