muddy the waters - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Confuse the issue, as in Bringing up one irrelevant fact after another, he succeeded in muddying the waters. This metaphoric expression, alluding to making a pond or stream turbid by stirring up mud from the bottom, was first recorded in 1837.