Vasse waterway | Science back seawater inflow to reduce algal blooms

Gates at the Vasse Estuary surge barrier will be opened this month to let seawater mix into the estuary in a plan to reduce algal blooms over summer.

Based on a three-year scientific trial carried out by the Department of Water and Environmental Regulation, the early and rapid input of seawater is calculated to reduce major algal blooms that occur each year over summer upstream of the Vasse surge barrier. 

The trial revealed that the timing, frequency and period of time the gates were opened produced different results, and the chosen opening strategy for this summer is the one that provides the most benefit to water quality.  

A study to better understand the relationship between water flows and the ecology of the Vasse Wonnerup wetlands is also underway.

The Departments of Water and Environmental Regulation and Biodiversity Conservation and Attractions have partnered with Murdoch University to carry out the two-year study to monitor seasonal water levels and water quality alongside aquatic plants, invertebrates, fish and birds. 

The internationally listed Vasse Wonnerup wetlands support tens of thousands of birds a day over summer, and the study will assess any impacts to the ecology through possible changes to the management of water flow into the wetlands.

Both projects are part of the Revitalising Geographe Waterways initiative.

Water Minister Dave Kelly said toxic algal blooms are a regular occurrence in the Vasse Estuary over summer, and poor water conditions have led to major fish deaths, with the most recent in 2014.

"It is a complicated artificial marine environment that requires a unique response to reduce the likelihood of algal blooms and fish deaths,” he said.

"Based on the science undertaken by the department, opening the gates at this time of the year to bring the estuary closer to marine conditions will provide the most benefit to water quality.

South West Region MP and Vasse Taskforce chairperson Dr Sally Talbot said the protection of the Vasse Wonnerup wetlands was an issue of importance for the local community.

"The wetlands study continues the commitments of the Vasse Taskforce to inform potential management actions with solid science,” she said.

“[The study] will be the first of its kind to link the hydrology and water quality of the wetlands with waterbirds and their food sources."

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