You don't need a license to fish in Crater Lake, but you will need to be agile. The only access is at the foot of the Cleetwood Trail, or on Wizard Island when boat tours are running.
The rainbow trout and kokanee salmon in Crater Lake were originally planted in 1888 by William G. Steel. They are now self sustaining, but you are welcome to keep as many as you like, with no size restrictions.
To protect the lake's purity, no organic bait of any kind, including power bait or salmon eggs, may be used; no private boats or flotation devices are allowed; and fish may not be cleaned in the lake.
There are fish in many of the Park's streams, too. Check out the, and good luck!