Visual. Look for flows of around 350 cfs. The Satsop gauge near Satsop gives you some indication of what's happening in the basin. The East Fork runs about 20% of this gauge. Historically there was a gauge on the East Fork (stn. 12034200 , 1957-1971, 65.90 sq. mi.)
Reports give the public a chance to report on river conditions throughout the country as well as log the history of a river.