Before discussing the problem, let me say thanks to Bruce Hubbard at On The Edge Watersports for explaining how to solve the problem and saving me a lot of money in the process.
Problem: because of the fires, ash and very finely ground plant material has washed into the lake and is now floating in random pockets across the water. The stuff basically has the consistency of coffee grounds. Most wakeboard boats suck water in off the surface to cool the motor and other components.
Watch your temperature guage closely as the cooling system can VERY QUICKLY become clogged. I know, it happened to me. Sunday, two other boats were tied up to the dock with overheated motors. I hear other boats overheated on Friday.
Here's how to unclog the cooling system-- at least on my Moomba. I believe it also applies to MC and Nautique: find the intake hose and follow it to where it connects into what I believe is the transmission cooler, a paper towel sized metal tube with two oil lines going into it.
At the front of the tube there is a grate. This grate is what is restricting the ash from flowing through and this is where my cooling system clogged up.
Your boat may be different, so check the mfg specs or with your dealer. BUT ONE THING IS FOR CERTAIN, IF BOAT TEMP RISES QUICKLY, IT IS NOT A BROKEN GUAGE.
Thanks again to Bruce for explaining the cause and the cure and saving me the time, hassle and expense of a trip to his place for repairs!