Idioms and Phrases with 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.