File:Flooding along the the Murray River, South Australia (MODIS).jpg

English: Wave after wave of heavy rainfall fell across a wide swath of southeastern Australia in the closing quarter of 2022, leading to extreme flooding in the Murray-Darling basin. According to news reports, the basin saw its wettest October on record in 2022, with rainfall totals nearing 150 millimeters—four times the average for the month and well above the previous record set in 1950.

By late November, the waters in the Murray River had begun to rise ominously. On November 21, the South Australia State Government declared a major emergency due to flooding, advising that peak flow near Christmastime was likely to result in 185 gigalitres of water flow downriver per day, with a chance of higher. That’s the equivalent of 48 billion U.S. gallons per day, or about 73,000 Olympic-sized swimming pools.

In early January 2023, flood waters were still cresting in some locations. On January 5, local news reported that a levee had been breeched by rising waters near Mannum, a town located on the west bank of the Murray River in South Australia. By January 7, peaking floodwaters had inundated most of the town, including flowing down Mainstreet. Because of the very flat topography of the Riverlands near the Murray, water recedes exceedingly slowly. Even after the crest is past, residents may wait weeks before they can begin to assess damages to their property-and months more before the river fully returns to its banks.

The long-term, vast flooding has also caused fish kills and toxic algae overgrowth in some regions, including in Lake Bonney, which had to be closed to recreation temporarily. Widespread “blackwater” events have been reported. Blackwater occurs naturally when floods wash leaves, grass, and other organic materials into waterways. This creates an abundant nutrient load, can be a good food source for fish and other aquatic life. As temperatures warm, these creatures become even more active, and their activity, along with decomposing organic matter, depletes oxygen in the water. This low-oxygen blackwater can lead to extensive fish kills.

On January 6, 2023, the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the flooded Murray River in South Australia. Below this is an Aqua MODIS image acquired about a year prior, on January 15, 2022, which shows a view of the Murray in a more normal year.