The urban area stretches across the areas administered by the city councils of Wellington, Lower Hutt, Upper Hutt and Porirua. The suburb of Porirua lies on Porirua Harbour to the north. Lower Hutt and Upper Hutt, collectively referred to as the Hutt Valley, are suburban areas to the northeast of Wellington City.Wellington's scenic natural harbour and green hillsides adorned with tiered suburbs of colonial villas are popular with tourists. The central business district (CBD) is close to Lambton Harbour, an arm of Wellington Harbour, which lies along an active geological fault, clearly evident on its straight western shore. The land to the west of this rises abruptly, meaning that many suburbs sit high above the centre of the city. There is a network of bush walks and reserves maintained by the Wellington City Council and local volunteers. These include Otari-Wilton's Bush, dedicated to the protection and propagation of native plants. The Wellington region has 500 square kilometres (190 sq mi) of regional parks and forests.