If you’re looking for a warmwater fly-fishing destination that offers angling all year long and is free to access and fish, then consider the Thermalito Afterbay, located in the Sacramento Valley near Oroville in the Oroville Wildlife Area. It is a huge, wholly man-made basin, and with 17 miles of shoreline and more than four thousand surface acres of water, it has become a hot spot for fly fishers targeting a range of species — largemouth bass, bluegills, green sunfish, black crappies, carp, even landlocked steelhead. The afterbay is part of the State Water Project’s Oroville-Thermalito Complex, which collects f lows from the Feather
River watershed to generate hydropower and supply water to agricultural users and to cities in Southern California. Construction on the afterbay started in 1965 and was completed in 1968. The afterbay, which has a maximum capacity of 50,000 acre-feet of water, is used to help regulate flows of the Feather River downstream from Lake Oroville, provide additional hydropower when the afterbay’s water is pumped back into the lake, and irrigate rice and grain fields in the area.
The water that flows from Lake Oroville is split in two at a diversion pool. One part turns toward downtown Oroville and becomes the Low Flow Section of the Feather River, and the other part is channeled into a canal that flows under Highway 70 and enters the Oroville Forebay, then arrives at the Thermalito Afterbay. From there, some of the water is released into the many canals that run out into the rice and grain fields and the rest goes back into the Low Flow Section of the Feather River to create what is called the High Flow Section.
The afterbay is quite shallow — it varies from 5 to 20 feet deep — and because it is used to control releases from the main reservoir into both the irrigation system and the Feather River, its level rises and falls. When the water rises, it floods the north and east ends of the afterbay. These ups and downs give the afterbay a tidal quality that the fish really like, and the ebb and flow of water over periodically exposed flats means that the afterbay is a food factory for warmwater fish. Big carp, in particular, love the north and east ends of the afterbay. They act like bonefish. Other species use the area to prepare redds for the spring spawn. You can fish the afterbay from the bank, but a watercraft will improve your ability to find fish. A motorboat, for example, is the best way to reach flooded structure, such as downed trees, but humanpowered watercraft are useful, as well. The afterbay is divided by the State Highway 162 causeway, which cuts across it from east to west. The smaller portion of the lake on the north side of the causeway has a speed limit of five miles per hour, so most of the big bass boats and jet skiers stay on the south side, where there is no speed limit. That makes the north part of the afterbay ideal for fly fishing from float tubes, pontoon boats, and kayaks. You can also launch a boat there, at a ramp that is just north of Highway 162 and east of Wilbur Road. The ramp is suitable for launching personal watercraft, as well.
Also suitable for personal watercraft are two other useful points of access to the northern part of the lake. One is on Tres Vias Road, off State Highway 99 just north of the Highway 162 intersection. There, you’ll find lots of cattails, floating lily pads, and flooded willows within float-tube range. The other access is the radio-controlled airplane field, which is reached from Wilbur Road. Again, there are cattails, lily pads, and flooded willows within float-tube range. (See “If You Go . . .” for more directions.) The southern side of the afterbay has launch access only from the eastern shore. At the Monument Hill Boat Launch, located off Highway 162 just southeast of the Highway 162 causeway, you can launch any type of boat you like. Another improved boat ramp is the Larkin Road Boat Launch, located approximately five miles off Highway 162. This launch isn’t used as much as the boat launch at Monument Hill, because it becomes very shallow when the water in the afterbay is low. A third launch, which is dirt and unimproved, suitable only for small boats, is situated where Wilbur Road dead-ends south of Highway 162.
All of these access points are free of charge. There are no boat-launch fees or day-use fees. Restrooms can be found at the improved boat launches and at the radio-controlled airplane field.
Fishing the Flats
Ryan Williams, an Oroville guide who fishes the afterbay quite often, targets bass in the flooded willows, lily pads, and cattails of the flats. Prime time is from late May all the way through September, as is the early morning and late evening, especially for top-water action. The southeast side of the lake has many islands, flooded trees, and brush, all habitat that holds bass, and he looks for places that have lots of weeds and sunken logs. He fishes small frog poppers, sizes 2 to 6, early in the season and larger poppers, size 1/0, as the summer wears on and the frogs grow, although in different parts of the lake, you can find larger or smaller frogs due to differences in their food sources, so he always carries a variety of sizes of popper. For top-water bass, Ryan fishes a fast-action rod, 7-weight to 9-weight. You need a big rod to get these fish out of the all that cover. Ryan and I had a long discussion about floating fly lines for this kind if fishing, and we came to the conclusion that it really didn’t matter what its taper is as long as the line floats well. We both use short leaders. Ryan likes a straight 0X tippet around 5 feet long. I use old tapered leaders leftover from trout fishing on Lake Almanor. They started as 7.5-foot 3X leaders, but I trim them back until they are tapered to around 0X. The tapered leader works better if there is a breeze on the lake. Top-end reels aren’t critical for this kind of fishing, because bass don’t make long runs. You just need decent drag and an ability to reel line in quickly. A large-arbor reel is perfect. Ryan doesn’t have a preferred frog popper pattern — he says that pretty much any frog popper works well. The one I have had great success with over the past couple of years is Rainy’s Lu’Au Frog, a fly-fisher’s Hula Popper.
Plop the popper down so it makes a large disruption on the water when first cast, then let it sit for a couple of seconds before making a short strip and pause. Then make slow strips until the popper gets all the way back to you. Fish often grab the popper as soon as it hits the water, or at the small strip right after the pause, or sometimes right at the boat when you are lifting the popper out of the water to make another cast. Ryan also likes to fish underwater knolls, drop-offs, and in front of the rocks that line the shoreline, and he prefers using the Float-n-Fly or FnF method with Balance Minnows or Balance Leeches, sizes 6 to 8. Because the afterbay is shallow, you don’t need to go deep — the fish can be in two to nine feet of water. I like to fish the underwater knolls with this tactic, too, using my fish finder to locate a knoll and to determine where the fish are holding — usually on the upwind side of the knoll, because the wind is pushing baitfish and other food items toward them. I position my boat with my back to the wind about twenty feet away from where the fish are and adjust my FnF rig according to the depth of the fish. I cast my rig just short of the fish and let the wind float it toward them and jig my fly. (To construct an FnF rig, see “The Floatn-Fly Technique with Thurman’s Floatn-Flies” in the January/February 2021 issue of California Fly Fisher.)
Because the bass usually will be holding in shallow water, you need a short tippet to make the Balance Fly effective. A couple of years ago, I was fishing the afterbay near the Monument Boat Launch and found a group of bass in two feet of water eating crappie fry. When I cast a fly on a sinking line into the bass and stripped it back, the bass would just part, opening a path for my fly to pass through, then go right back to eating the fry. I switched to an FnF rig with only a foot of tippet material and immediately hooked up. I sat there in my boat and caught eleven more fish before the bite ended.
All the water that holds bass also holds panfish ranging in size from five or six inches to dinner-plate diameter. The gear for panfish is just your typical trout rod — a 9-foot 5-weight rod with a floating line and a 7.5-foot leader tapered to 4X. I use a heavy tippet because I have had bass grab the small poppers I fish for panfish. Small balsawood or foam popping frogs are the flies of choice.
Fishing the Rocks
The afterbay was constructed with a rock crest dam, and the rocks that line much of the shoreline hold bass waiting to ambush their prey. The rock dam forms all of the south and west shore, and the Highway 162 causeway is built on rocks, too. The hardest part of fishing the rocks is getting to them. For motorboats, it is no problem, but for fly fishers using float tubes, pontoons, or kayaks, it can be difficult. The best places to launch are the Larkin Road and Monument Hill boat launches. The access at Tres Vias Road will also get you to the northern tip of the rocks. The rocks vary in size, and they hold bass year round. Low-light conditions and cloudy days seem to be the best time to find bass active along the rocks. I position my boat so I can make cast right to the rocks using a sinking or sink-tip line, then let the fly drop down the slope of the rocks while I strip the fly back. I vary the strips, starting with a slow strip and ending with a fast strip, trying to figure out what the fish want. There are miles and miles of rocks, so keep moving to find fish. The grabs are fantastic. But the rocks can grab your fly, too. You definitely will lose flies fishing rocks — that is just part of the game.
My gear for fishing the rocks is also a fast-action 7-weight to 9-weight rod, but with a fast-sinking Type 6 or 7 full sinking or sink-tip line. My favorite line is the Streamer Tip, a floating line with a 10-foot fast-sinking tip rated Type 6. Again, the reel you chose isn’t all that important. It just holds the line. I fish a short, level 0X fluorocarbon leader. You need to be able to haul those bass out of the rocks, and the fluorocarbon resists abrasion. My flies of choice are crayfish, minnow, and leech imitations. I like flies that are heavily weighted — I want to get them down fast. My favorite crayfish imitation is Mercer’s Poxyback Crayfish, size 4.
Carp
Carp are plentiful in the afterbay. I have fished for carp there only a few times, though, so I reached out to Zack Thurman, a fly tyer and carp guru at The Fly Shop in Redding, and asked him how he would fish for carp at the afterbay. He recommends sight fishing from a boat you can stand up in, with one person spotting the fish and running the boat and one person casting. For carp, Zack likes a fast-action 8-weight rod with a weight-forward floating line and a long, 10-to-12-foot fluorocarbon leader tapered to 2X or 3X. For a fly, he recommends Darin’s Hoover Moover in gold, size 4. Carp are very wary, and I have had plenty of carp spook on me at the afterbay. You need to make a good cast the first time out. It’s a game with a learning curve I haven’t really climbed yet, but if you’re one of the fly fishers who is haunted by the ghost of the flats, you can be sure to find plenty of them in the Thermalito Afterbay.
Steelhead
There actually are steelhead in the afterbay, too, despite it being a shallow, warmwater fishery. The Feather River Fish Hatchery is allowed to release only a certain number of steelhead smolts into the river, and when it has excess smolts, they plant them in the afterbay, usually in the winter or the spring. In December 2022, the hatchery planted 129,000 yearling steelhead smolts. The smolts initially range from seven to nine inches long and can be found in the cold water coming into the northeast side of the afterbay from the forebay canal. Many anglers also fish for them in the canal itself. There is a buoy line across the mouth of the forebay canal in the afterbay so boats do not travel up the canal. The cold water penetrates far into the afterbay, though, and the smolts that don’t get caught grow rapidly in the cold water of the inlet. I have seen pictures of 18-to-22-inch fish.
The smolts are planted at the Wilbur Road Boat Launch and are easily accessed by fly fishers using personal watercraft. It’s a great place to take kids to have lots of fun action. The hatchery announces the plants on their website and also notifies the Oroville Mercury News and the Chico Enterprise Record. (See “If You Go…” for the Feather River Hatchery website address.) I have had success fishing a Chan’s Chironomid Bomber in black and red, size 10 or 12, under an indicator. These fish aren’t shy, and they eat anything they can.
Give it a Try
The Thermalito Afterbay is off the radar of many fly fishers, but it has a lot to offer, from bass to steelhead. Give it a try sometime.
Fave Flies for the Thermalito Afterbay
Rainy’s Lu’Au Frog Popper (although almost any frog popper should prove productive)
Mercer’s Poxyback Crayfish
Darin’s Hoover Moover
Chan’s Chironomid Bomber
If You Go…
To reach the first of the three personal-watercraft access points on the northern side of the lake, from Highway 99 just north of the Highway 162 intersection, turn east onto Tres Vias Road. There will be a locked gate with parking to the left and to the right of the gate. Please don’t park in front of it. You can pack your float tube a short distance on an access trail that leads about one hundred feet to the water.
To reach the second access point, the radio-controlled airplane field managed by a group called the Oroville Air Corps (5525 Wilbur Road), turn north from Highway 162 onto Wilbur Road. You will cross the water canal that connects the forebay with the afterbay. The road to the access will be on your left just past the canal. There is a sign indicating it. Once at the parking lot, you can access the north side of the afterbay.
The third launch point, known as the Wilbur Road boat launch, is reached from an access road running north off Highway 162 and opposite Luds Way. It is also a popular spot for bird watchers.
For water levels in the afterbay, phone the Department of Water Resources recorded phone line, which is updated every weekday morning: (530) 534-2307.
For information about the planting of steelhead smolts in the Thermalito Afterbay, go to the website of the Feather River Hatchery in Oroville, https:// wildlife.ca.gov/fishing/hatcheries/feather-river.
The Butte County Sheriff’s Office does boat patrols on the afterbay. Please follow all boating regulations and wear a personal floatation device at all times.
There is no camping at the afterbay. It is part of the Oroville Wildlife Area and is day-use only.
There are no fees to use the boat ramps, day-use areas, and restrooms. The lake’s groundskeepers and custodians ask that you place trash in the trash cans located around these facilities and clean up after yourself. These are the same folks who take care of Riverbend Park in Oroville.
The closest fly shops are located in Chico: Sierra Stream and Mountain, 847 West 5th Street, Chico, CA 95928; phone (530) 345-4261; website, www.sierrastreamoutdoors.com. Fish First Fly Shop, 766 Mangrove Avenue, Chico, CA 95926; phone (530) 343-8300; website: www.fishfirst.com.
For a guide who works the afterbay, contact Ryan Williams. Phone (707) 365-9891; website, https://flyfishcnv.com; email, rwguideservice@yahoo.com.
— Lance Gray
