Here is a photoset of the Plain of Six Glaciers Trail
and the Iceline Trail
Both are *generally* good trails, bot on PoSG, there is a ledgey section (sometimes with water running across it) that is less stable (see here
) though I think you can skip most of it by taking the horse trail if you prefer. Near the top of the trail, there is a set of switchbacks getting to the teahouse, and the trail degrades on them (here
). Also note that if you want to go beyond the teahouse to the Abbot Pass viewpoint, the trail is smaller and less well-kept.
Just be aware that in early- to mid-September, either of those trails could easily have snow, so you'll want to monitor the conditions.
Really, everything in Waterton is awesome, so I'd jsut choose trails on what sort of length of trail you're looking for.
If you've never been to Waterton, make sure to do Bear's Hump. It's a wee little touristy trail above the townsite, and only takes an hour or something, which would lead a lot of people to skip it. Don't. The view across the Waterton lakes really is spectacular, and it's well worth the little jaunt. You definitely want to make sure to drive around and see some of the little things like Red Rock Canyon.
If you want a break day, Crandell Lake is a 1-2km walk in (so you can carry pretty much anything), and is a great place to laze around and swim for an afternoon. It's much warmer than the Waterton Lakes.
If you're going to do one big hike, I'd recommend Carthew-Alderson
before the overhyped Crypt Lake. (Actually, Akamina Ride is #1, but has a scramble step and isn't generally a good trail, so you can save that for next time). Just make sure you look at the photos and judge its stability and width for yourself, as opinions differ
as to the difficulty of the trail.
For most of what you'd be doing, there are lots of options. Lineham Falls, Rowe Lakes, Bertha Falls/Lake, etc. are all well worth it.
If you're camping, you'll want to weight competing factors. the townsite campground is right in the middle of everything, but is basically a field with spots, and everyone right next to each other. The other campgrounds in the park are a little better, but have a lot of bear issues. If you don't mind driving a little extra at the start and end of each day, I highly recommend the Belly River Campground
. You have to leave the park, and drive around to the edge to get to it, but it is much larger, and has really nice treed tentsites that are secluded and pretty.
But then, in September, there aren't that many people around any more, so it might not be a big issue.