Crossing the Smoky River can range from easy when the water is low - ankle to calf deep, to treacherous with high water levels such as waist level or possibly higher. Water levels are usually lower by the end of August when the winter snow melt has subsided. However, even then, they will typically be lower in the morning and higher in the afternoon due to glacier melt during the day. Water levels are also higher after rains.
Regardless of water level, the current is swift. Best to use trekking poles when crossing such fast flowing water.
This alternate Smoky River crossing is done where the Smoky River has spread out, and is therefore shallower, on the gravel flats about 400 meters (0.25 mile) downstream (northwest) from the flagged hikers crossing on the Moose River Route: Smoky River Crossing to Moose Pass.
When one gets to the Smoky River, simply wander downstream looking for a good place where the water is well spread out and looks shallower—easier to see more of the rocky bottom. By the end of August, it can easily be as low as only high ankle deep at this alternate Smoky River crossing, while it is knee deep at the flagged hikers crossing along Moose River Route: Smoky River Crossing to Moose Pass.
After finding a good place to cross, go for it. Yes, the water is cold, but it's not bad at all if one keeps moving.
After crossing, head back upstream on the gravel flats to find the original trail - Moose River Route: Smoky River Crossing to Moose Pass, across from where you left it on the opposite side. On the southwest side, there is a big log with a cairn at the end. On the northeast side, look carefully for a hiker sign.