Bramble Bay in the north-west of Moreton Bay, shows clear signs of poor health an imbalance because of human activity. The water is brown and muddy from topsoil washed from gardens and construction sites and the upper catchments of the Brisbane River. After heavy rain, water flowing out of the Brisbane River usually carries a load of sediment (mud), as well as nutrient and sewage pollutants. This plume of water spreads out, mainly to the north into Bramble Bay. The tidal currents are less vigorous in the western part of Moreton Bay, so these sediments don�t disperse easily. Because Bramble Bay is so shallow, the small silt particles are kept in suspension by wind and wave action. The waters of Bramble Bay are only clear for a few weeks during the winter months, because of still conditions. The turbidity of the water has had dire consequences for aquatic animals in Bramble Bay. Because light no longer penetrates the cloudy water, the once abundant seagrasses have gone, as well as the turtles, dugong and other creatures which fed on it. Prawns, which can tolerate most environments, are still plentiful.
In addition to the cloudiness of the water, high concentrations of nutrients (particularly nitrogen) lead to algal blooms in Bramble Bay. These are visible as a greenish tinge in the brown water or along the shore. The nutrients which cause the algal blooms come not only from the suspended sediments, but also from the sewage discharges from Luggage Point and Hays Inlet that are �trapped� in Bramble Bay. Bramble Bay is the most degraded embayment of Moreton Bay. This is primarily a result of the high levels of nutrients and sediments that are transported into Bramble Bay from the Brisbane and Pine Rivers. Approximately 63% of the total sediment load and 51% of the nitrogen load into Moreton Bay is predicted to enter via the Brisbane River alone. Significant proportions of nutrients are also transported into Bramble Bay from Hays Inlet and Cabbage Tree Creek. Also contributing to Bramble Bay�s poor condition is poor flushing, the area possessing the longest residence time of Moreton Bay (59 to 62 days). Bramble Bay is within a General Use Zone of Moreton Bay Marine Park and contains areas within the Moreton Bay Ramsar site.