Frank, I want to urge you to consider doing the entire length! It is not as strenuous as Half Dome, it is
really a worthwhile adventure of a hike.
As for the water, it was not cold at all in September. The water temp was not something I even noticed or remember, so it had to be ok. I do recall, though, that the air temp was chilly for the first half hour, until we warmed up with the hiking. The only thing that is unusual is that you really need to embrace walking right through the water.
It was funny, I was in a group of 6, and four blasted ahead in the first few miles where it was all dry. But as soon as we hit the parts where we waded, they really slowed down. Timid, I guess. We caught up with them, and then were waiting for them often. By the end of the day, they were tramping along at the same speed. I think they finally adjusted to the different style of "hiking".
I looked up my post in the "Ten US DayHikes" thread. I nominated The Narrows in that thread, and included a number of links. You should definitely browse all of them.
"The Narrows" in Zion National Park
