Probably just a layer of water in the bottom of the carb. Remove the air filter, dump out all of the gas and oil, then turn the mower upside down on some
old cardboard in the yard, and leave it upside down all afternoon in the sun, and let all of that moisture evaporate, then this evening, fill with fresh fuel
and new 30 wt. oil, maybe even a new air filter, and plug.
And you should be ready to mow.