I was in the back of the boat assisting with boards, ropes etc. My son jumped in and my wife turned on the engine. My son yelled to me that there was a lot of "smoke" coming out of the exhaust.
I looked down and saw steam coming out of the exhaust. Not a lot but enough to throw me into panic mode. I looked at the temp gauge from the back of the boat and saw it was just above the 180 mark for the first time!

After shutting down the engine I jumped in, went under the boat and half of the intake was blocked by what looked like algae. I checked the filter next to the v-drive and it was almost fully packed with algae.

We had never been out in the stuff before and now we know to avoid it. There wasn't much but that is all it took. Took it out the next day and everything was fine. Need to run a compression check but it seems fine otherwise. No steam, no water in the oil, no oil in exhaust, runs well. I let the motor cool by opening the hatch for 30 minutes rather than shock it with cold water

So an observant observer may have (and most likely did) save not only the day but the motor as well.

Is there any audible alarm for these gauges or senders? As much as I hate to admit, I am not watching the gauges full time but that is one I look at a lot. It can creep up quickly.