John Wesley on Joshua 3:17

Stood firm - That is, in one and the same place and posture; their feet neither moved by any waters moving in upon them, nor sinking into any mire, which one might think was at the bottom of the river. And this may be opposed to their standing on the bank of the water when they came to it, commanded, Jos 3:8, which was but for a while, 'till the waters were divided and gone away; and then they were to go farther, even into the midst of Jordan, where they are to stand constantly and fixedly, as this Hebrew word signifies, until all were passed over. The midst of Jordan - In the middle and deepest part of the river.