Millions of dead, decomposing fish have filled much of a river in southeastern Australia, which is being hit by a severe heat wave, local authorities said Friday.

The New South Wales state government said “millions” of fish are dead in the Darling River near the village of Menidi, the third time since 2018 that such a phenomenon has been seen in the area.

Videos posted on social media show boats sailing through a thick layer of floating dead fish that makes the surface of the water almost invisible.

“It’s truly horrible, there are dead fish as far as the eye can see,” Graeme Makrab, a resident of Menidi, told AFP, speaking of the “incalculable” environmental consequences.

According to the local government, fish populations in the river had increased significantly after the recent floods, but the waters have since receded.

“The death of these fish is linked to the low level of oxygen in the water (hypoxia) because the flood waters are receding,” the local government explained in a statement, adding that the heat wave is exacerbating this phenomenon.

Previous mass fish kills in Menidi had already been attributed to the lowering of the river level, but also to the spread of a toxic alga over almost 40 kilometers.

Menidi, a village of 500 inhabitants has been severely affected in recent years by floods and drought.