Unless something changed, I'm fairly certain that the park's CFS limit is 600cfs as a maximum (supposedly set because that's the limit that local kayaker / rescuers said they would go in), and a minimum of 150cfs (supposedly we will disturb the fish at lower flows). Since the river has a wide range of daily flow fluctuation, this could severely limit the number of boatable days if strictly enforced.
The technicality of the whitewater is another debate (thread/dead horse/can of worms), and; the addition of a sieve, a new portage, multiple "new" sketchy logs, blind corners, cold water, long days, very cold weather, shallow/rocky flows, all within the confines of a very deep canyon, create for a river that doesn't fit very neatly into our current rating system (see other threads). It is a mentally and physically challenging run.
Fifteen miles of low flow, relatively low gradient river takes a long time to complete, and walking makes it worse, and the shuttle is long, and delayed if checking in with the park service same day. Start early, and travel quickly. It's probably freezing cold at the put-in, and the water was snow the night before, so a drysuit is highly recommended. Cold temps, and shallow water, lead to many broken boats in the first six miles. Boat repair kit is mandatory.
If the park see's that our community of river runners can complete the canyon safely and self-sufficiently, then I believe we will have more access granted, and less high-flow restrictions.
Truly one of the greatest kayak runs ever. Some eye candy; The Colorado Kayak Chronicle: Kayaking the Zion Narrows with the Arrogantly Challenged