If you begin at the upper airstrip there is a short section of shingle braids down to the first gorge. 200m of class III-IV boulder gardens lead you to the sieve where the entire river goes under a boulder. Be wary of this and be sure to make the exit point which comes at you quite quickly. Portage on the left.
Below the sieve a continuous steep section leads down to the top of Jumboland flats, where giant mountain faces, hanging snow fields and craggy waterfalls provide a fabulous backdrop to the next 4km of class III-IV paddling.
Below this is a long class V section with rapids that vary in style from 3-4metre multi tiered drops to tight technical boulder gardens. Portaging is easiest on the left and you can get in and out where you please and paddle the drops you want and walk others.
Below this section the gradient eases markedly to class III for about 3km down to the Siberia confluence at Kerin Forks. No whinging about the 90 minute class I-II paddle out from here though as hundreds of trampers every year walk for three days to get into this valley to see the scenery and for kicks you can always paddle up behind a few and frighten them on the way home.