As human populations increase, more housing, roads, malls, parking lots and highway are built and this often means that streams and wetlands are filled in, built on or paved over. Chinook and coho are the two species of salmon particularly impacted by urban development. Coho salmon are found all year round in stream systems and they are known to inhabit even very small streams.
Loss Of Habitat
Streamside trees and vegetation are essential to maintain stream temperature, to control rain runoff and to add nutrients to streams. Few municipalities have working policies or by-laws to protect streamside areas with adequate buffers from industrial and residential development. More than 80 percent of the marshlands in the urbanized Lower Fraser River have been lost to development, wetlands that are critical to juvenile salmon as they acclimatize to their future saltwater environment.
Stormdrains in urban areas carry harmful toxins from car and truck exhaust flushed in from roads and highways. Careless or uninformed householders dump car wash detergent and leftover chemicals into stormdrains, hundreds of which empty directly into salmon streams. Industries illegally dump toxins into the stormdrain system.
Stream diversions, culverts
Many streams have had their stream channels physically altered or moved to make way for housing developments and shopping centres. Others have been redirected into underground culverts, destroying any useful fish habitat. Some culverts under roadways are completely impassable to salmon.
Loss of stream flows
Buildings, roads and parking lots stop natural rainwater from soaking into the soil to replenish groundwater supplies. This loss of water can cause streams to dry up in the late spring and early summer when juvenile salmon need adequate waterflows to make their journey to the sea.