What were the frequent mishaps on the rivers between Iffley and Oxford?

From the text:

"... the current drives you on to the right bank, and then on to the left, then it takes you out into the middle, turns you round three times, and carries you up stream again, and always ends by trying to smash you up against a college barge."

"... as a consequence of this, we got in the way of a good many other boats, during the mile, and they in ours, and, of course, as a consequence of that, a good deal of bad language occurred."