Tell me you didn't just pull it out and try to start it..?
Here's what's wrong if you did...
The air filter is waterlogged.
the crankcase has water in it.
The cylinder(s) have water in them.
The electrical components are wet.
If it fell in chorinated water rust has begun inside and out.
Let alone the other non-engine components.
Which may be alright.

You need to empty the water; clean/inspect/oil the inner parts; replace gaskets etc.

It can probably be salvaged; but by someone who is adept with tearing down and rebuilding/repairing small engines and machinery.

It must go to the doctor now.

Kidding aside the longer you wait to take it to a good commercial equipment dealer the worse the prognosis because chlorinated water = corrosion.
-br

I take it you have already removed it from the pool : ) That is the first step.

I would not panic, but I would:

Replace/clean the air filter.

Hit all the electrical connections with compressed air.

Drain and clean the fuel tank. Flush the fuel lines. At least drain the carb, but disassembling the carb and cleaning would be best.

Take out the spark plug and get any water that might be in the cylinder out. Pour a teaspoon of oil in the cylinder and rotate the engine a few times.

Change the oil. If you can get it to start, let it run for a few minutes and change the oil again..then I'd repeat the oil change routine until it comes out clean.....

Others may have a better idea, but this is what I'd do.....

Good luck.

1st thing to do is to hose it off with fresh water, lots of it. Then dry it out and change the oil.

Well the water rushing up the hot exhaust to the valves and pistons can't be a good thing. But, as suggested above and if it is a flat head design it will be easy to remove the head and clean, dry check things out, this includes full fuel system clean-up. Course you will about a case of carb. cleaner to clean it up if shyt an't warpped.

If you got one of them chineze knock-off motors just spend the 129 bucks and get another.

That happened to me too, but mine's electric, and it fell into my chlorinated pool. Well it eventually just dry out on its own?

This just happened to me too. I have an electric pressure washer and it fell into my chlorinated pool while it was running. Will eventually just dry out on its own?

Gregd -- THANK YOU for your extremely helpful comment. My Simpson gas powered generator fell in the pool.

It is running again thanks to you. Here is what I did.

1. Removed the air filter.

2. Drained the fuel tank.

3. Removed spark plug and turned the unit upside down to allow any remaining water that might be in the cylinder out.

4. Drained the old oil out.

5. Hit all the electrical connections with compressed air.

6. Added new oil. Poured a teaspoon of oil in the cylinder.

7. Added fresh gas.

8. Rotated the engine a few times. Engine started and died.

9. Drained oil and found it was milky colored. Added new oil.

10. Keep repeating steps 8 & 9 until oil is clean.

11. Replaced air filter.

12. Replaced carb.

13. Started and ran for 3 minutes.

14. One final oil change.

Good luck!