Overheating

I had a similar problem on my 2000 SN, but solved it with bfootr's advice. I had searched long and hard (and unsuccessfully) for the vane pieces downstream of the pump. Finally found them on the inlet side!

Again, no.

Guilty as charged here also.

That never happens.

(Extreme sarcastic tone)

The fake lake supplies water from your hose with 35-60 pounds of pressure.
Your Raw Water Pump depends on suction to pull water from the lake.

If you are overheating at the lake there are a few things to verify and check.
As already mentioned if you had an impeller fall apart in pieces those pieces all need to be retrieved. You will find them spread out in your cooling system.
The only real way to get them out is to remove the hose and start flushing each of them.
From the boat inlet all the way to your exhaust manifolds. The thermostat sometimes catches a few pieces and one member reported finding chunks inside his main engine block water pump.
While doing all this you might consider adding a Timmy T, affectionately named after our own TRBENJ who invented and shared his how to tips.   The Timmy T is actually much easier to hook a hose to and it only works if your raw water pump is providing suction so it more accurately acts like pulling water from the lake.
All hose connections on the inlet side including your water strainer must be sealed tight or the raw water pump will pull air rather than water.
If you have any air leaks you will struggle to pull water to cool properly.

To find the posts that give this information it helps to use Google or DuckDuckGo, type in your request, TimmyT   Correctcraftfan and search. The forum here is great but the search funtion is not so great, the google search is more effective.
Mark

Same thing happened to me. Probable cause is a bad impeller and/or obstruction to or from the water pump. In my case, most of the vanes of my impeller had broken off and were lodged in the water pump INLET hose. Would run at proper temps with the Fake a Lake attached (due to the added water pressure and simply idling, but would over heat at the lake especially when accelerating). Check the impeller first and see if there are any obstructions.