touch bottom

Reach the lowest point, as in During the recession the economists kept saying that we hadn't touched bottom yet. This metaphor for reaching the ground under a body of water has been used since the mid-1800s.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.