River flows were the highest since 2011.

National river inflows were well above average at 115 mm or 882,000 GL; 29% above the 2000–2020 average and 75% more than the previous year.

River inflows were near or above average almost everywhere. High to extremely high river flows occurred in catchments in southwest WA as well as along the Victorian and NSW coast and in the Border, Gwydir and Namoi Rivers. 

Tropical lows caused major flooding in the Herbert and Lower Burdekin Rivers in Queensland in January and in the northwest in February. 

In March, major flooding occurred in several coastal NSW catchments, especially in the Hastings, Camden and Manning Rivers, as well as in the Gwydir and Condamine rivers in the northern Murray-Darling Basin. Flooding occurred again across large areas of NSW and Queensland after high rainfall in November and locally in Victoria and South Australia. 

There were no large algal blooms or fish kills in the Murray-Darling Basin in 2021.

Storage in the Murray-Darling storages increased, with combined storage in the five largest storages increasing from 57% to 90% of capacity, reaching levels last seen in 2013.

Reservoir storage in the Ord system in the Kimberly region increased after three years of decline, from 29% to 58% of capacity.

Urban water supplies increased for all cities. The Sydney and Canberra supply systems remained near full capacity, while storage increased in Melbourne, Brisbane, Perth and Adelaide.

National annual area inundated

The national extent of wetland flooding was greater than the previous year and reached the greatest total extent since 2016, but it was still 9% below the 2000–2020 average.

Wetland extent was the greatest since at least 2000 in several catchments along the southern WA and South-east coast, and in the Border, Gwydir and Namoi rivers in the northern Murray-Darling Basin. Wetland extent was below-average in only a few isolated catchments.