Passamaquoddy Bay is enclosed by a tangle of islands, peninsulas, and narrow passages that make it look, from the air, like a puzzle missing a few pieces. The southernmost point is West Quoddy Head in Lubec, Maine. From there the bay stretches northeastward past Campobello Island, engulfs Deer Island, and reaches the New Brunswick mainland at L'Etete. Three entrances connect it to the Bay of Fundy: Letete Passage northeast of Deer Island, Head Harbour Passage to the southeast, and Quoddy Narrows between Lubec and southern Campobello. The Head Harbour Passage serves as the deepwater entry, and its sovereignty remains a point of contention. Both governments agree it is Canadian water, but the United States maintains that international law grants commercial vessels a right of passage, while Canada asserts the authority to regulate traffic -- a dispute sharpened by proposals to route liquefied natural gas supertankers through the passage to terminals on the American shore.

The international boundary through Passamaquoddy Bay has been disputed since the American Revolution. The Treaty of Ghent, which ended the War of 1812, included provisions for commissioners to divide the bay's islands between the United States and Great Britain, yet confusions persisted for decades. The Passamaquoddy Bay Treaty of 1910 finally established the boundary as a series of seven connected straight lines running from a point between Treat Island and Friar Head southward through the bay to the middle of Grand Manan Channel. Even this formal resolution left room for argument. The narrow passages between Maine and the islands -- Western Passage, Friar Roads, Lubec Narrows, Quoddy Narrows -- host the international line itself, meaning that fishermen, ferry operators, and pleasure boaters cross back and forth between nations with every tack. The largest community on the bay proper is St. Andrews, New Brunswick, though the twin border towns of Calais, Maine, and St. Stephen, New Brunswick, sit just upstream on the St. Croix River.

A border running through busy, island-studded waters practically invites smuggling, and Passamaquoddy Bay has obliged for centuries. After the American Revolution, an illicit trade flourished across the bay's many channels. The peak came in 1808 during Jefferson's Embargo, when smugglers moved tens of thousands of barrels of American flour into New Brunswick in defiance of the law. During the War of 1812, the contraband flowed in reverse -- British manufactured goods slipped south into American hands. After the war, the primary commodity shifted to gypsum from Nova Scotia, which was deposited directly into American vessels on or near the border. What made Passamaquoddy smuggling distinctive was its openness. Officials and locals on both sides winked at the trade, viewing it as an economic necessity rather than a crime, and actively discouraged interference from authorities in distant capitals who lacked appreciation for the bay's particular realities. The border was a legal abstraction; the bay was where people lived and worked.

Passamaquoddy Bay sits at the entrance to the Bay of Fundy, home to the highest tides on Earth, and the water moving through its passages does not behave gently. Between Deer Island and Eastport, the collision of tidal currents creates the Old Sow whirlpool, the largest tidal whirlpool in the Western Hemisphere. The bay's tides also make it a subject of recurring interest for tidal power generation, with proposals dating back decades for harnessing the enormous volumes of water that surge through its entrances twice daily. The city of Eastport, Maine, perches between Passamaquoddy Bay and Cobscook Bay to its west, a community shaped entirely by water -- its currents, its commerce, and its rhythms. From the air, the bay's complex geometry of islands, passages, and headlands reveals a landscape that has resisted human efforts to simplify it, whether through treaties, tariffs, or straight lines drawn on charts.