What temp is too hot to target Muskies in?

When is it too hot to target muskies (water or air temperature)?  I was thinking of trying for them, but I've seen people say it is too hot if you plan on catch and release for a muskie.  Should I wait until mid-september when the weather and water temps are cooler?  Is there a number I should wait for it to drop below?

As stated below, 80 degrees is the accepted number.

For me personally?  78 is when I shut it down.  That's when I've noticed that fish have a harder time being released.  Last 5 years or so, when the water gets around 78, I water release my fish.  I do not net them, nor do I take them out of the water.

I've spent too much time babysitting fish, taking them to shaded, cool water and sitting there waiting for them to get enough strength to be released.  It's just not worth it to me.

Anything over 80 degrees is generally considered too hot. Any time it's above 75 extra caution should be used when handling them as they are even less durable than normal.