Forgot to address your question re rotenone.
I don't know about the temps, but would suggest you consider an alternative. I know you don't want to loose what water you have but since it is very shallow, rather than rotenone, why not rent a trash pump over the weekend and just pump it out. That way there would be no concern about chemicals, the fish would be perfectly eatable or even re-usable if you choose to place in holding tanks. You would need to be sure to get it completely drained, however, just as you would have to get complete coverage with the rotenone. I know a lot of folks have used rotenone and I'm probably viewed as overly conservative, but I'm just really cautious about using chemicals that kill everything.
