Contributed by Michael Reeder
What It's Like
Classic whitewater in an intimidating canyon.
Scouting / Portaging
Scouting is possible for most rapids. The hardest rapid of the run is impossible to portage, some other rapids could be portaged if wood was in play.
~3 hours to show yourself down, 1 hour if you know the lines.
When to Go
Typically runs in August, however can be caught at runnable flows all summer long and into the late fall if you pay attention to weather and snowpack.
16.5cms↓ (Dec 5 04:40)
There Yoho has been described as being a run that only has 1 rapid, but its 6km long.
One of the most classic runs in the area, the Yoho provides continuous, quality whitewater in a breathtaking canyon. More intimidating and consequential than it is technically difficult, the Yoho's frigid, chalky-white water contains dozens of class 4 moves back to back to back and enough small eddies to catch your breath and warm up your hands in. The inaccessible nature of the canyon, continuous nature of the whitewater and must-run crux puts this run solidly in the class 5 range despite most individual moves feeling more like 4/4+. Numerous stories of Heli-evacuations and heinous swims add to the lore that surrounds this river and the respect with which it is treated.
Takkakaw Falls (Photo by Rich Kemble)

Starting off at the base of Takakkaw falls the Yoho meanders down some class 2 for a kilometer or so before the pace picks up. The river narrows and the gradient increases which creates a style of whitewater best characterized by lots of strong currents and reactionaries to keep your nose on top of and ride. Shortly after a narrow gap with a slight undercut on the left come 3 Deuces. 3 Deuces has multiple lines at different flows, but all are fairly narrow and worth having a look at, especially if you are not familiar with it or are checking for wood.
3 Deuces (Photo by Garrett Quinn)

A handful of really nice rapids later comes another narrow gap with a big eddy on the left just after it. The sunshine eddy. Since the Yoho is most often run in the morning at the low point in it's diurnal fluctuation and the canyon walls are so high, this happens to be one of the few places where sunshine reaches the river. This eddy is a great place to warm up the hands, especially since the crux, Pandora's Box, is not too far downstream. A couple of nice moves and one of the best boofs on the river separate the sunshine eddy from the scout eddy for Pandora's. It is a small eddy (2 boats max) on river right. Pandora's is a few hundred meters long and can only be partially scouted. The big, flat-topped rock in the middle near the bottom of the rapid is a bit undercut and the channel to the left of it is also undercut/has an overhanging wall that has been responsible for at least 1 heli-evac. Too far away from the scout to see properly, but just upstream of the flat-topped rock is a large hole that angles and pushes towards the rock. The ideal line is to stay right of the big, flat-topped rock.
Scouting Pandora's (Photo by Rich Kemble)

The next major rapid after Pandora's is the Keep, a 6-8 foot ledge that is most vertical drop on the river and should be run on the right. Immediately after the Keep comes Tunnel of Love (possibly "Tunnel of Fear" according to Stuart Smith's guidebook), a long, narrow hallway that beautifully frames Castle Mountain in the background. From here to the takeout is more Yoho goodness with too many boofs, eddies and rapids to name. 

There is a gauge located just before the hairpin switchbacks on the road to Takakkaw falls. Normal runnable flows are from 20 to 13 holes showing on the post that the gauges keep getting ripped off of. It does channelize quite well so could definitely be run lower. 
High flows make for some very continuous whitewater and are most enjoyable when you already know the lines.

A rough correlation can be found online by using the Kicking Horse gauge where flows around 60-80 cms are a good indication that the Yoho could be in, however a lot of tributaries enter below the Yoho. The Yoho is fed by fairly high elevation snowmelt. This means that even if the Kicking Horse is quite a bit higher than 80 cms, cold weather up high could have the Yoho at prime flows. 

Due to the fact that it is fed by snowmelt, hot weather can bring the river up quickly. The low point in the day seems to be somewhere between 6 and 10 A.M. with most days not seeing a dramatic increase in flow until after 12:00 noon. Be warned though that the river can rise quickly on a hot day and late-morning laps that run into problems can have those problems compounded by quickly rising levels. 
Evening laps, especially on cold days in the summer, or warm days in the fall can be glorious.

Put in: Parking lot at the base of Takkakaw Falls

Take out: A small pullout a few hundred meters before the switchbacks on the road to Takkakaw Falls

P.S. Buy a park pass. Support Parks and if you get stuck in the canyon you don't have to pay for the Helicopter rescue.