Lake Quag is drained by the mighty Velverdyva river system, one of the largest rivers in the entire Flanaess and the largest river in Perrenland. Indeed if one boarded a boat on Lake Quag, one could journey down the Velverdyva all the way to the Nyr Dyv, passing Greyhawk City itself, all the way to the sea. The river is regularly choked with traffic and small communities hug almost the entirety of the river's banks.
The Velverdyva exits Lake Quag at Quag Quay, a notorious braid of shingles, backwashes and groundings at the southern foot of the lake. At any one time there are at least a dozen flows from Lake Quag into the Velverdyva proper, however only two or three of these are ever navigable. The first thirty miles of this river are quite treacherous.
Lizard men, trolls and the odd marsh giant inhabit these washes and backwaters, making travel through this region perilous. An experienced pilot can find the main braids of the river and avoid these perils of course, but pilots are not cheap and river pirates lurk at the entrance points to the lake.
Currently the main channel used for river trade between the Velverdyva and the communities of Lake Quag is known as the Right Flow.
Further downriver the Velverdyva becomes both stable and broad, being relatively safe to travel. The one exception to this is the Gate of the Velverdyva, the canyon that separates Perrenland from the Highfolk, and the Clatspurs from the Yatils. Here the river is both swift and deep and an experienced pilot is needed to make the journey safely.
Once in Highfolk, the river flows past Verbeeg Hill. The waters make the land here very fertile and eels are commonly collected from the river.