Pregolya

Pregolya , also spelt as Pregola (German: Pregel, ) is a river in the Russian exclave of Kaliningrad. It starts as a confluence of the Instruch and the Angrapa and drains into the Baltic Sea through Vistula Lagoon. Its length under the name of Pregolya is 123 km, 292 km including the  Angrapa. The basin has an area of 15,500 km². The average flow is 90 m³/s.Euler's Seven Bridges of Königsberg problem was based on the rivers' bridges in what is now Kaliningrad.
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