In late September 2015, I hiked part of the trail in the incredibly beautiful Lónsöræfi in southwestern Iceland, near Vatnajökull. The easternmost segment of the trail requires fording Hnappadalsá (Satellite/aerial view). Some people by-pass this section by driving a nearby mountain road (which skips a very spectacular part of the trail, and doesn't look any less scary!). Still, Hnappadalsá contained rather a lot of water:
One common advice is to wait for the morning, when the river might contain less water. As far as I'm aware, this is based on the (reasonable) expectation nights are colder, there is less melting, and therefore less water. However, this river is not glacier-fed: there are only tiny icefields upstream, there was hardly any snow left, and it was a cool autumn day. I didn't have the patience to wait for 16 hours, I crossed and survived, but it was quite scary and it certainly wasn't wise of me to cross¹.
Most of the water in the river was not meltwater. Is it still useful to wait for the morning?
¹ I'd probably have flown to the lake soon enough, I did consider crossing by swimming through the lake across the river, but didn't have the right gear.