Albert Barnes Commentary Judges 7:24

"And Gideon sent messengers throughout all the hill-country of Ephraim, saying, Come down against Midian, and take before them the waters, as far as Beth-barah, even the Jordan. So all the men of Ephraim were gathered together, and took the waters as far as Beth-barah, even the Jordan." — Judges 7:24 (ASV)

The waters - The streams which run from the mountain district of Ephraim into the Jordan in the district of Beth-shan, forming great pools and marshes, which the Midianites fleeing south would have to cross before they could reach the Jordan fords.

All the men of Ephraim - They had taken no previous part in the rising against Midian; nor had Gideon, of the smaller tribe of Manasseh, presumed before to summon his more powerful and arrogant brethren of the great tribe of Ephraim .