However, it's quite likely that the salt content and other contaminants present in sea water make it unpure so as to be unfit for their reproduction. Freshwater lakes, however, including the GIANT ones in North America (which NYC is not that far away from)...
The very first draft of the script ends with Billy luring all the Gremlins to a greenhouse with one he has trapped in a toolbox (in the script, the Gremlins will go to any lengths to regain a lost member of the group). However, waking up in the hospital later, he realizes he never opened the toolbox. Cut to a worker cleaning out the greenhouse, seeing a nice brand-new toolbox, and putting it in his truck, only for him to get scared and toss it away when funny noises start coming from inside. It lands in a lake. . .
