A large fish kill has occurred in southern Lake Macquarie, the NSW Environment Protection Authority said.
EPA officers investigated the incident at Mannering Park, collecting fish and water samples for laboratory analysis to uncover what caused the death.
"EPA and council officers observed about 100 dead fish of various species and sizes. Field officers also noted greying around the gills, which suggest oxygen depletion," an EPA spokesperson said.
"A decrease in oxygen content in water is a natural event that can cause rapid fish deaths.
"The EPA has been out in the field over the weekend collecting further water and fish samples, and seeking to identify any potential pollution sources."
Fish kills can be linked to flood water. When a lot of organic material washes into a waterway, its rapid decay can consume dissolved oxygen from the water.
If this dissolved oxygen drops to very low levels, this can cause "hypoxic water", which can stress and kill native fish.
If the community has further information that could help the EPA's investigation, call 131 555.
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