Pacific salmon can no longer access hundreds of kilometres of spawning streams or much of their historical floodplain habitat after decades of urbanization and development in the watersheds of British Columbia’s Lower Fraser River.

The study by researchers at the University of B.C. focused on 14 salmon populations in the lower Fraser, Canada’s most productive salmon river.

It mapped where an estimated 85% of historical floodplain is lost or inaccessible to the fish due to dams and dikes.

Riley Finn, the lead author and a member of the conservation decisions lab at U.B.C., says the vegetation-rich habitat lost would provide food and protection from predators for the young fish.

He says it’s particularly important for salmon species that remain in fresh water after their eggs are hatched, such as chinook and coho.

The study, published in the journal Ecosphere, found more than 1,200 barriers, such as road culverts, are blocking access to about 64% of stream habitat that would otherwise be naturally accessible.

Finn says the study is a foundation for ongoing work to identify priority areas where removing in-stream barriers would produce the greatest benefits for salmon.