Hundreds of dead fish washed onto the beach in Gulfport on Wednesday night, but state officials and environmental activists disagree on how they got there.
The state Department of Marine Resources said it appeared to be nothing out of the ordinary.
A Gulf Restoration Network official, however, said it looks like a clear sign of a 'fish kill' from commercial fishing vessels.
The 200 to 300 fish washed ashore just west of the Island View Casino.
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DMR spokeswoman Melissa Scallan said scientists examined the fish and concluded they died of natural causes as early as Monday.
The smell was one of the first tip-offs.
"Those fish were in an advanced stage of decomposition," Scallan said. "They were pretty deteriorated when we saw them. That leads us to believe they died a couple days ago and just washed up."
DMR officials also factored in the number of fish found.
"We look at the numbers, too. There will be a lot more fish than what we saw Wednesday if it was a fish kill -- like thousands," Scallan said.
F.J. Eicke, spokesman for the Coastal Conservation Association Mississippi, disagreed with the DMR.
He said a likelier explanation is the fish escaped the nets of a commercial vessel and died in the process. He said he counted six fishing boats Wednesday off the coast where the fish were found.
"I suspect they got out of the nets somehow and washed ashore," he said. "The boats were there, then they weren't. Then the fish washed ashore. This is a fish kill. One plus one equals two."