The Seine

Paris sits at the first of six horseshoe turns in the riverbed, each looping back on itself in a 180-degree turn as the water heads downstream. Combined with the relatively mild grade from Paris to the ocean--Paris is only about 250 feet above sea level--this means that once a great volume of water reaches Paris, the land itself provides little incentive for it to move on quickly. And that volume is great, since the entire basin covers an area over 48,000 square miles, filled with streams and rivers that feed into the Seine.