Same for R, or riffle, a place where water's flow has sped, dancing to create a frothy turbulence. And the same for side channels, which are separated from the main bar by gravel, masses of tree roots or wood jams, and which slow the water to nearly stagnant. A rock smaller than a baseball is gravel. Bigger than a baseball yet smaller than a basketball makes it a cobble. Call that rock a boulder.
Some rocks look pocked with acne.
It's just caddisflies, aquatic insect grazers that are a sign of a healthy stream. From previous research, the scientists have a hint what to expect when salmon negotiate the 17 miles of habitat made off limits by the Landsburg diversion dam. Salmon returning in the fall and winter to spawn and die provide pulses of nitrogen and phosphorus, essential nutrients for the stream and for the ecosystem. Add salmon and, at the base of the food chain, the community of primary producers like algae increase in number. Insect populations boom.