COFFS Harbour resident David Lloyd is at a loss to explain a large slick of discoloured water he reported floating off Boambee Beach.
David noticed a large tract of dirty water near the rocks at the northern end of Boambee Beach below the Coffs Harbour Deep Sea Fishing Club on Sunday morning.
"At first I thought it was an oil spill, it was quite large, covering about two football fields, I immediately spotted it from the beach," David said.
Collecting samples of the brown water, David reported the incident to Marine Rescue Coffs Harbour.
While the substance smells like a man-made petroleum substance it settles at the bottom of a jar, ruling out the theory it is oil.
"As you can see krill, which I scoped up in the jar have died in the dirty water.
"I've also ruled out tuna oil, given it didn't disperse it just hung around in the water near the rocks and was very slimy to touch.
"It was so thick you couldn't see through it."
If you have an explanation of what the slick may have been add a comment below.
Update your news preferences and get the latest news delivered to your inbox.