We have lived in FL since '84' and have been tubing, skiing, swimming, canoeing etc. in lakes, rivers and oceans. Is it 100% safe? No, but you have a far greater chance of getting injured or killed in a car crash then you do by a gator attack.
Yes, if there is a body of water in FL then there is a good chance that a gator is in it. The "rare" gator attacks happen by the edge of the water and not in the middle of a lake. Thousands of Floridians are in the lakes daily during spring and summer and if it was so dangerous you would be reading about it all the time. I have been canoeing on rivers that have gators, I have been golfing and seen gators, so I guess I should not do that either.