Oh My, is it going to burn up SF water in the lake? Must be a hellofa hot fire, maybe like the super hot fire SF so deserves.
When a forest fire burns the drainage in the miles above a lake, the next rains brings a sludge of mud, ash, soot, burned logs, etc. All kinds of crap wash down. It does it to the point that it can utterly choke a lake and any water delivery system coming from it.
In recreational lakes it’s a nuisance that takes a couple of years to clear out well. In a water supply lake its a much bigger likely problem.