WATERSPORTS -- Whitewater enthusiasts are expecting a warm welcome from Washington's Tieton River along US 12 west of Yakima this weekend.

A large gathering of rafters and kayakers -- private and commercial -- is gearing up from across the region to take advantage of the annual "flip-flop." 

The annual September release of water that's been warming all summer in Rimrock Lake has begun in order to feed water to downstream crop irrigation needs as well as to boost salmon spawning.

The "flip-flop" term comes from the fact that the increased water down the Tieton helps make up for the reduction of flows in the Yakima River.

The result is an opportunity for great whitewater boating in the month of September.  

• By the way, if you're an angler, the flip-flop spells the beginning of good fall trout fishing in the Yakima.

Boaters will come in droves to go with the flow from launch sites below Tieton Dam. The river runs down the generally sunny east slope of the Cascades.

Flows of 1,000 cfs to 3,000 cfs are considered ideal in the Tieton, which hit the 1,000 cfs mark on Aug. 28 and exceeded 2,000 cfs today.

• See updated flow information.

Runs of 11 to 15 miles that have been too rocky and bumpy to boat all summer will fill with rushing water, ushering rafts and kayaks through almost continuous Class II to III rapids before the Tieton flows into the Naches River.

Since summer heat has dried up most of the region's whitewater for the season, many river runners consider theTieton River the last summer run.

The river has a steep gradient, dropping 58 feet per mile. The Tieton is not considered to be great for novice boaters because of its steady rush of whitewater.

Campers note: Fire restrictions could be in effect.