Halifax's official harbour limit for navigational purposes is delineated by a line running from Herring Cove on the west side of the main channel, to the northern end of McNabs Island, then from McNabs Island across the Eastern Passage to the actual community of Eastern Passage on the east side of the island. The harbour is marked by an extensive network of buoys and lighthouses, starting with Sambro Island Lighthouse at the harbour approaches, the oldest operating lighthouse in North America.