Grade A is in sheltered water. You should be capable of paddling 20km (12 miles)per day in Force 2/3 conditions.
Grade B is in more challenging waters and may include tidal streams, exposed headlands, and open crossings between islands. You should be capable of paddling 25km (16 miles) per day in up to Force 4 conditions. A Four Star paddler would feel comfortable on such a trip.
Grade C You should be capable of paddling in more difficult conditions than Grade B for a longer time.
International River Grading System
GRADE 1
Moving water, unobstructed and without technical difficulties. There may be small waves and riffles to challenge the paddler.
GRADE 2
Waves, small stoppers and other minor obstructions to avoid. Eddies and cushion waves may be strong.
GRADE 3
Waves, stoppers and technical difficulties are more severe. There may be drops and powerful constrictions. The main distinguishing factor of Grade 3 water is that the paddler will have to follow a recognisable route to avoid obstacles and hazards.
GRADE 4
Severe waves, drops, stoppers and other obstructions. The route is not easily recognisable and will usually require careful inspection from the boat or bank. Grade 4 encompasses a wide range of rivers, from those with pool-drop rapids to those with extended continuous rapids; so there is a huge variation in difficulty. It is common to distinguish easier grade 4 rapids by grading them as 4- and harder rapids as 4+ (or in some cases, 3/4 or 4/5).
GRADE 5
Extremely difficult rapids with precise and technically demanding routes to be followed. Stoppers, currents and waves will be powerful and inspection is essential.
GRADE 6
All of the above carried to extremes. Grade 6 usually means unrunnable rapids, which may just be possible in certain conditions.