3123 The 650-mile-long Vistula River, the longest in Poland, gathers in the country’s southern highlands. It courses northward through both Krakow and Warsaw before ending where this photo was taken, about 15 miles east of Gdansk, carrying the winter floes seen here into the Baltic Sea. The nation’s iron-blue artery is one segment of the E40 waterway, a system of naturally occurring rivers augmented by manmade canals that linked markets from the Black Sea to the Baltic for nearly 200 years. After World War II, however, the waterway, which also cuts through Belarus and Ukraine, was abandoned as a commercial conduit. Now the three countries hope to restore it. The economic upsides are obvious for all three countries but especially for landlocked Belarus, which would gain access to two of Europe’s busiest ports. There’s an environmental plus, too: By cruising on currents, barges release just one-third the CO2 that freight trucks do, and are four times more...