High nutrient input and poor tidal exchange in the Peel-Harvey Estuary has caused blooms of microalgae and macroalgae for many years. Green algae have been found on the beaches since the 1970s. The blue-green algae Nodularia spumigena bloomed during the 1980s in the Peel Inlet then developed in the Harvey Estuary in the early 1990s. Macroalgal or 'weed' removal has been occurring near the populated northern shores since 1989.

Those algal blooms impacted on people using the estuary in several ways. Commercial fishing harvests were difficult because the algae were caught in fishing nets. Recreational use of the estuary was limited for long periods due to toxic algal blooms and people living within 10 km of the estuary were at risk of a virus transmitted by mosquitos.

The opening of the Dawesville Channel (DC) in 1994 increased salinity and allowed for a greater exchange of nutrients out of the estuary. This reduced the problem of pre-DC algal blooms and the estuarine water quality showed improvement.

Algal blooms still occur, as nutrient inputs have not diminished significantly; however, the species differ in response to water quality changes since the DC opening.

• in 2000, a bloom of filamentous blue-green algae, Lyngbya spp., was found in Roberts Bay. The Lyngbya sp found in Moreton Bay, Queensland, can be toxic and is irritable to the skin. Analysis revealed the Peel-Harvey Lyngbya sp to be non-toxic at that time, although future blooms would need to be tested for toxicity. Lyngbya sp has been found in Lake Goegrup and the Serpentine River in late 2006 and 2007.
• a marine algae, Acanthophora spicifera, has been found south of the DC since 2007 when complaints were received about a 'spiney' seaweed in the area.
• higher salinities in the Peel-Harvey Estuary have not completely prevented Nodularia sp from blooming. It has been identified in the less saline reaches of the Serpentine River around Lakes Rd bridge during the summer months.
• a 'cappuccino-like' scum has appeared in the Murray River in recent years. This algal scum is named cappuccino scum due to its 'creamy' appearance and 'coffee' colour. It is currently unknown which algal species is responsible for producing the scum.

The water quality and algal species and distribution have not stabilised since DC and trends are developing. The current snapshot builds on the overall algal picture in the Peel-Harvey Estuary and provides valuable information used in the management of this environmentally and economically valuable waterway.

References

Environmental Protection Authority 2008, Water quality improvement plan for the rivers and estuary of the Peel-Harvey system - phosphorus management, Environmental Protection Authority, Perth, Western Australia.

Robb M, Hosja W, Kidd A, Norton S, Parker A, & Ridley P 2009, Occurrence of algal growth in the Peel-Harvey 2004-2008, unpublished document for City of Mandurah State of the Environment Report, Department of Water, Perth, Western Australia.

URS 2007, State of Play Peel-Harvey eastern estuary catchment environmental assessment discussion paper, report prepared for Department of Water, Perth, Western Australia.