The "Lower Sac" is a world class blue ribbon tail water in Northern California. This river gets both wild and hatchery salmon/steelhead as well as a great population of very healthy wild native trout (Central Valley Steelhead). 
The water supplied by Shasta lake is pulled from a lower section and keeps the river, often flowing at 10k cfs, a constant temperature year round. This constant cold water supply supports a high population of mayflies(bwo, pmd) but the food menu is quite diverse, caddis, stoneflies, sallies, salmonflies, scuds, sculpins, midges are some of the food sources for these fish. Salmon eggs & Sucker Fish eggs make up another part of their diet. With over 30 miles of river to float this makes the lower sac a top trout fishing destination in the United States.