Fresh water = insufficient electrolytes for galvanic or stress corrosion corrosion. Both bolt & hanger are marine grade stainless (so galvanic not an issue anyway). You're fine.
I suppose if algae were growing straight on the bolt as the rock was drying and you were getting tons of drying cycles in the hot sun then you might in theory get some corrosion (assuming algae like this even exist in Sierra lakes) - but with 316 ss it'll be super unlikely.
How tall are the routes. I can hold my breath just over four minutes (great party trick) and I say we go have a run at those routes when the water comes up. I'd like to have a go at the first underwater ascent. Call me. I'll bring speedos for both of us.
Unless you are near an area with lots of salt or salt water or very wet all year long (which rules out about 95+% of all climbing areas) galvinic corrosion is not a problem. Galvinic corrosion is one of the most misunderstood phenomenons in the climbing community. Sure you should try to use stainless anchors whenever possible, but most mixed metal anchors aren't the ticking time bombs that many people fear.