The Lower Mainland in British Columbia is protected from tidal and seasonal flooding by a series of 600km of dikes and over 400 tide gates. Tide gates occur wherever a stream meets a dike and function like one way culverts that allow freshwater to flow out while preventing flooding of valuable low land agricultural, commercial and residential areas.

 

During the spring freshet, high river flows from snow melt can prevent the tide gates from opening for long stretches of time (weeks to months).

 

We found that water quality behind some of these gates fell below the minimum requirement of water quality set by the government of British Columbia. Specifically dissolved oxygen concentrations were too low to support native fish!

 

Hypoxic areas extended over 100m upstream. These hypoxic dead zones are a potential chemical barrier to fish movement, including salmon migrations.

 

With an estimated 500 aging floodboxes in the lower Fraser River, there is a need to further assess the cumulative effects of floodboxes on estuary habitat in order to balance protection of both people and fish.