Muddy the waters, issue, etc.
Definition 1 of 1

Figurative Use
Used metaphorically to describe actions that complicate understanding, not actual water.

When she started blaming the internet, it really muddied the waters of our argument.
Avoid in Formal
Though common, it may be too informal for academic or highly professional settings.

In a formal report, instead of 'muddied the waters,' try 'created ambiguity'.
Negative Connotation
Usually implies that the action taken to complicate matters was avoidable or unnecessary.

The witness's contradictory statement muddied the waters of the investigation.
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