There aren't many of them, but they're there: flathead catfish the size of a Labrador retriever in Idaho's Snake River. Flatheads aren't always easy to catch, but they are a major quarry (think of them as your own personal Moby Dick) and along with abundant channel cats make an Idaho catfish safari complete. Late May and early June, as water temperatures climb above 60 degrees, is your best window of opportunity to hunt a mix of three- to five-pound channel catfish and the massive flatheads in the three reservoirs that stretch between Boise and Hells Canyon. Fish the upper ends of Hells Canyon, Oxbow and Brownlee reservoirs with prawns, sucker meat, night crawlers or big bass jigs fished deep. Flatheads are often caught on lures and bait used specifically for channel cats. You'll need stout tackle. Idaho's state-record flathead, a 581/2-pounder, was caught in Brownlee in 1994; the all-tackle record is a 123-pound behemoth caught in Kansas in 1998. But even hard-core catfishers say hooking-let alone landing-a big flathead takes some luck. "We estimate that flatheads probably don't make up much more than five percent of the catfish population in the Snake River reservoirs," says Jeff Dillon, fisheries manager for southwestern Idaho. "They're fairly rare, but occasionally a real monster will be caught by someone fishing deepwater bass jigs or while fishing for channel cats." The best place to target both species of catfish is the Snake River upstream of Brownlee. Biologists monitoring tagged fish have found that numbers of cats swim as far upstream as Swan Falls Dam to spawn. Cast to areas of flat water and tails of islands around Clarks Island and Marsing Island and upstream at Map Rock, Lava Point and Noble Island. Contact: Jeff Dillon, Southwest Idaho fisheries manager (208-465-8465); Howard's Tackle Shoppe in Nampa (208-465-0946).