The Sea North is only associated with the Land Northward:
8 And it came to pass that they did multiply and spread, and did go forth from the land southward to the land northward, and did spread insomuch that they began to cover the face of the whole earth, from the sea south to the sea north, from the sea west to the sea east. (Helaman 3:8)
There has been some confusion over the location of the Waters of Ripliancum:
8 And it came to pass that he came to the waters of Ripliancum, which, by interpretation, is large, or to exceed all; wherefore, when they came to these waters they pitched their tents; and Shiz also pitched his tents near unto them; and therefore on the morrow they did come to battle.
10 And it came to pass that the armies of Coriantumr did press upon the armies of Shiz that they beat them, that they caused them to flee before them; and they did flee southward, and did pitch their tents in a place which was called Ogath. (Ether 15:8,10)
The battle between Shiz and Coriantumr originated at the West Sea (Lake Erie/Niagara Gorge), so we know that the Waters of Ripliancum were not Lake Erie/Niagara Gorge. The Waters of Ripliancum were on the north, since the armies retreated from the north toward the south.
Some may feel the interpretation “large to exceed all” was referring to the wonderfully large Niagara Falls, but the falls did not exist then.
The largest body of water – “to exceed all” from eye level is Lake Ontario. You can trace the borders of all other bodies of water in Western New York from eye level, but not Lake Ontario. The Sea North of the Nephites IS the Waters of Ripliancum of the Jaredites, our current day Lake Ontario.