context: There are 13 natural reserves in Warsaw – among others, Bielany Forest, Kabaty Woods, Czerniaków Lake. About 15 kilometres (9 miles) from Warsaw, the Vistula river's environment changes strikingly and features a perfectly preserved ecosystem, with a habitat of animals that includes the otter, beaver and hundreds of bird species. There are also several lakes in Warsaw – mainly the oxbow lakes, like Czerniaków Lake, the lakes in the Łazienki or Wilanów Parks, Kamionek Lake. There are lot of small lakes in the parks, but only a few are permanent – the majority are emptied before winter to clean them of plants and sediments.
question: How far from Warsaw does the Vistula river's environment change noticeably? 
answers.text: 15 kilometres About 15 kilometres 15 kilometres