The force said people had been out on the river in boats and although they "understand their willingness to help, it is not a safe environment and could hamper the co-ordinated search".

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The Coast Guard will patrol the river in boats with machine guns mounted on their bows.

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In Varanasi, her guests travel on the river in flower-decked boats with musicians instead of just watching from the riverbanks as other travelers do.

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The early British planters could not find workers locally so labour contractors collected not just men, but women and children too, from distant parts of India and sent them on boats up the Brahmaputra river which flows through Assam.

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On Wednesday, officers using inflatable boats were checking waterways and river banks for clues as to the girls' whereabouts, and police divers were on stand-by.

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The number 2 tram on the Pest embankment to Vigado Square, where boats leave each hour for 45-minute trips up and down the river.

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In Bangladesh, border officials said they believed several boats with Rohingyas on board were waiting to try to cross the river from Burma.

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The Port of London Authority (PLA) imposes a 12-knot (14-mph) limit west of Wapping, which means that boats can show their exhilarating 30-knot cruising speed only on the eastern stretches of the river.

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