bass
I think the unstable water conditions lead to this issue in Hagg specifically. For me the best bass fishing comes early and late in the year out there - when water levels are pretty stable. I love spring Hagg, when the water is up at full pool, and there's lots of flooded grass and wood. Once the lake starts dropping, the fish get put off and it becomes a hunting game - I've had my best success following shelves and fishing points, along with any submerged wood I can find when the water drops. Tanner creek on the north end can still be good. Deep water by the dam can also be good for both large and smallmouth. Lipless cranks, deep running cranks, and soft plastics are my go to baits at that point.
In the fall, once irrigation has ended and the levels normalize, the fish will move shallow again. I've had great days in September and October throwing top water almost all day long. Zara Spook Jr becomes a favorite bait at that point.
When the surface temps climb toward 80, I try to find springs and creek inlets as well - access to cooler fresher water seems to draw both the trout and the smaller fish bass feed on.
Good luck dude, Hagg bass are finicky at best on a good day out there due to the pressure - if you get them in an eating mood it gets pretty glorious, but it seems rare!
I have a lot of trouble at hagg in summer too. A lot of people talk about the summer pattern for large mouth in general being either shallow cover or deep. Hagg is plenty deep, easily 100 feet at the damn end, but once the water starts to fall there is next to 0 shallow cover. Just muddy bottom for what seems like forever. I have a feeling you could find them suspended some place out in open water but that's tough in a kayak. You'd spend a lot of energy looking. I was there in September 2016 for the purpose of just mapping the bottom because the water was so low you could see everything at the upper end, and found it quite uninteresting. The creek channel of scoggins Creek may be a good place to try if there is still water in the flooded grass back that way, and the channel has a sheer wall that they may be able to ambush against. But I've not tried that this late into the year. Once I discovered the smallie bite on the Willamette in summer, I haven't been to hagg much after spring!
Before my Sunday trip I went ahead and spent $15 for a one year subscription to the Navionics app for my phone so that I could use it while fishing. I know I could use the web page but the app is nicer and seems a lot faster. That worked great and I highly recommend it if you don't have great maps already.