‘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 Bethbarah, even the Jordan.'
Not wanting the enemy to escape too easily Gideon sent fast messengers to Ephraim and asked them to move down and guard the fords. The flight would take time, for some would at some point stand and fight, others would make for the hills until the way seemed clear, while their panic meant that they had not been ready for the journey and many would be on foot. So they would not move as fast as the speedy messengers, whom Gideon probably already had standing by.
“So all the men of Ephraim were gathered together, and took the waters as far as Bethbarah, even the Jordan.” Ephraim were quick to respond. They stood firm by the covenant. They knew something of what had been happening but had clearly not been so affected, if at all, by the invasion. But they were ready to support their brothers.