I know where you're talking about, but haven't used a put-in in that area. I've read that some of the put-ins in the tributaries to Jamaica Bay turn into mud flats at low tide. Also, Jamaica Bay can be subject to sometimes high tidal currents and cross winds. It's a fun place to paddle, though.
I'd suggest looking over the paddling.net launch site map, as well as the map at NYC Water Trail:
Personally, if paddling Jamaica Bay I like the put-in at the south end of the Cross Channel Bridge, on the north end of Broad Channel. Also, I hear the put-in at Floyd Bennett Field is really nice.
You might also consider talking to or visiting the Sebago Canoe Club, which has a small rowing component on Jamaica Bay - nothing like getting some local wisdom:
Good luck, and watch out for crazy people in jet skis and speed boats....
Canoe Pack Liner
Kayak Motor Kit
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