Charles Ellicott Commentary Joshua 4:7

"then ye shall say unto them, Because the waters of the Jordan were cut off before the ark of the covenant of Jehovah; when it passed over the Jordan, the waters of the Jordan were cut off: and these stones shall be for a memorial unto the children of Israel for ever." — Joshua 4:7 (ASV)

The waters of Jordan were cut off before the ark of the covenant. —Observe that the act is indirectly ascribed to the ark of the covenant: