Pools are also used as feeding areas, especially for big trout. The fish will cruise or patrol in a particular pattern when the feeding period comes. And because stream banks are often undercut in pool areas, pools tend to be places where large woody debris (logs) get added to the stream. Large woody debris greatly improves habitat for fish and insects. Aquatic insects that are often found in pools include dragonfly larvae, scuds, aquatic worms, damselfly larvae, cranefly larvae, and leeches.
Finally, it is important to know that there are different kinds of pools: meander-formed pools, log-enhanced or rootwad pools, boulder-formed pools, and bedrock-formed pools. All are critical for the survival and successful reproduction of migratory salmonids like bull trout. In short: if you want good trout habitat, make sure you have pools.