Well.....the first thing is to give us some sort of clue where it came from. What state? What area? Only then might someone be able to help you ID the rock and what they know about it.
Also...see how it knaps. It might or might not need to be treated in any way.
Third, if it does need heat treatment, whether it was in water or not is irrelevant more or less. Standard heat treatment requires heating the rock just below the boiling temp of water for 24-48 hours to remove any water from the rock (that's about 200 degrees since water boils at 220). After that, the actual heat treating would begin and a conservative start would be to try 350-400.
Lots of time wet rock or rock that has been just dug up knaps better than dried out rock - weird, but many swear by soaking their rock before knapping. So, knap some of that stuff then reveal to us some info on geographics, then someone may be able to help.
Cool you found rock! Looks promising. Just looking it could be hornstone or one of the NY state cherts, but who knows?