I think with the rain the Austin area got yesterday and maybe tonight, I would head west and fish the Llano. My go to spot for wading the Llano is starting at the confluence of the Llano and the James Rivers (30.64907, -99.25000). You can wade down quite a ways and wade up to where to rivers meet. You can also head further up the James and wade a lot (depending on the water level). Last year I fished the James up past the bat cave (30.56545, -99.32981) and caught plenty of Guads and a couple Rios.
I haven't fished Castell, but there is probably plenty of wading available there as well. The guy that owns Castell Store, and much of Castell, is nutty MAGA douche.
If I am making a full day of it, I'll leave before dawn and drive way out west and then fish several spots on the way back.
If you haven't picked up a copy of Aaron Reed's Fly Fishing Austin & Central Texas, do you self a favor and get one. He sets out 50 different wades in 21 rivers/creeks within a couple hours drive from Lady Bird Lake.