Estuaries of Georgia Strait

EstuaryEstuaries occur where rivers meet the sea and salt water mixes with fresh as the tide goes in and out. Because so many rivers and streams flow into the waters of the Salish Sea, the whole area is a huge estuarine system. Estuaries are the most biologically productive ecosystems on earth, more productive than grasslands, forests, and even areas of intensive agriculture.

Although estuaries make up less than 3% of BC’s coastline (as of 2004), 80% of our wildlife depend on estuaries for survival. For example:

  • River nutrients are passed up the foodchain to predators such as bald eagles.
  • Migrating birds need extensive wetlands when winter snow and ice cover fields, ponds and streams.
  • After hatching upstream, salmon fry depend on estuaries to grow and acclimatize to salt water before heading out to sea.
  • Salmon also depend on estuaries at the end of their life cycle, when they return to rivers to spawn.

Estuaries are essential to humans as well. Estuary silt is an irreplaceable pollution filter, cleansing inshore waters and removing toxins such as sulphur dioxide from the air.

The Fraser River delta is our region’s largest estuary. It is the only coastal waypoint of its kind between California and Alaska. Birds from 20 countries and three continents depend on it for overwintering or for rest and sustenance during their long annual migration along the Pacific Flyway.

BC Nature Trust has identified three nearby estuaries as being internationally significant for migratory birds:

  • Comox (1300 hectares)
  • Denman Island (2500 hectares)
  • Cowichan-Chemainus (2000 hectares)

Losing our estuaries

Losing any intertidal wetlands would have a severe impact on migratory bird populations and the health of our region – and some species are already endangered. Nevertheless, coastal estuaries are threatened.

Around tVancouverhe Strait of Georgia, the biggest pressure on estuary habitat is from urban development and sprawl. Over recent decades, Georgia Strait’s estuaries have been disappearing under golf courses, condominiums and trailer parks.

Pollution from the forest industry can also harm fragile estuary ecologies:

  • Toxic wood preservatives from sawmills (even inactive ones) can damage salmon habitat.
  • Bark and sunken wood waste from log booms decay, which removes oxygen from the shallow water. This smothers bottom life and suffocates fish.
  • Toxic chemicals from pulp mill effluents get into the aquatic food chain, becoming contentrated in larger animals at the top of the chain.

Examples of such losses :

  • Nanaimo Estuary: > 50%
  • Cowichan Estuary: > 50%
  • Fraser Estuary: 82%
  • Burrard Inlet: 93%