Learn the "SWAMP" anchor

I first saw this anchor in action at Smith Rock in central Oregon about 15 years ago. I was in the “mouth” on Monkey Face, belaying my partner on the airy aid pitch. While waiting, a Canadian guide popped up from another route, and set up this anchor in about 15 seconds to fix the rope for his partner. “DANG”, I said, “That’s pretty slick, I've never seen an anchor built like that before.” He said it was common practice in Canada and the UK, where he had lived for a while.

I'm sure this rig has some different names of different parts of the world, but in the US it’s known as a “SWAMP” anchor, which stands for “Shelf Without A Master Point.” (I think this name is kind of lame, but I don't have anything better. If you know it by a different name, please tell me.)

The SWAMP anchor is simply an overhand knot tied in about the middle of a sling. Each end of the sling gets clipped to an anchor / bolt, and a master point locker gets clipped to the two loops made by the knot.

Fast to make, simple, minimal gear, decent load distribution, no extension, and completely redundant, pretty sweet!
Downsides: 1) no shelf (but those are a bit overrated, IMHO) and 2) might be a bit hard to untie after loading, depending on the sling material. (Some folks seem concerned about lack of redundancy if one leg were to be cut and then a heavy load applied to the other leg. In a recreational climbing scenario I think this is extremely unlikely to happen, but in other anchor applications it might be a concern.)
Tying a standard cordelette style rig with a 60 cm sling usually doesn’t work, because the knot and loop take up too much of the sling material.
A girth hitch master point solves pretty much the same issue and is easier to untie. Try them both and see which one you like better.
As seen in the video, this is only used on a 2 piece anchor.
It’s completely redundant and non-extending, but like all statically equalized systems, does not do so well in the load distribution / equalization department. However, if you have a well defined direction of pull, and all you've got to build your anchor is one shoulder length sling, this can be a good #CraftyRopeTrick to have in the toolkit.

Let's address one common objection right off the bat: how strong is this? Yes you are completely reliant on that one knot holding. Good news: #SuperGoodEnough!

I tested this configuration with Ryan Jenks / HowNot2.com in spring 2023, and the results are below. About 20 kN in Dyneema, and about 28 kN in nylon. Being that your rope is going to break around 16 or 18, I think 20 is just fine.

Here’s a nice video posted by Josh Beckner, an IFMGA certified guide, covering just about all aspects of building 2 piece anchors. The SWAMP is demonstrated starting at 11:10.

And, here’s a photo sequence showing how it’s done.

Clip a single runner to one bolt or gear placement.