Rahab told the spies that Jericho had heard how the LORD dried up which waters for Israel?

Answer: The Red Sea

Rahab said, "We have heard how the LORD dried up the waters of the Red Sea before you when you came out of Egypt."

“For we have heard how the LORD dried up the waters of the Red Sea before you when you came out of Egypt, and what you did to Sihon and Og, the two kings of the Amorites across the Jordan, whom you devoted to destruction.”— Joshua 2:10 (BSB)