"Blue infrastructure" refers to urban infrastructure relating to water. Blue infrastructure is commonly associated with green infrastructure in urban environments and may be referred to as "blue-green infrastructure" when being viewed in combination. Rivers, streams, ponds, and lakes may exist as natural features within cities, or be added to an urban environment as an aspect of its design. Coastal urban developments may also utilize pre-existing features of the coastline specifically employed in their design. Harbours, quays, piers, and other extensions of the urban environment are also often added to capture benefits associated with the marine environment. Blue infrastructure can support unique aquatic biodiversity in urban areas, including aquatic insects, amphibians, and water birds. There may considerable co-benefits to the health and wellbeing of populations with access to blue spaces in the urban context. Accessible blue infrastructure in urban areas is also referred as to blue spaces.