The government has said it "may never find the cause" behind the deaths of thousands of shellfish off the North East and North Yorkshire coast.
Environment minister Mark Spencer said that while the unexplained mass die-off had been "catastrophic", scientists may never identify the source.
Since late 2021, thousands of marine life including crabs have washed up between Hartlepool and Whitby.
A report said a disease or parasite new to UK waters may have been responsible.
The mass die-off on 40 miles (70km) of coastline saw shellfish washed ashore between October and December 2021. Dying creatures were "twitching" and displaying lethargic behaviour.
For the past 15 months, a range of potential causes behind the deaths have been identified, but all of them largely ruled out.
They include natural algal bloom, dredging of the River Tees and the industrial chemical pyridine.
Labour MP for Stockton North, Alex Cunningham, called for a further investigation as Mr Spencer gave MPs an update on the mass die-off on Thursday.
Mr Cunningham said: "As there is still no definitive cause, nothing can be ruled out and only a further in-depth, transparent scientific study will give our communities the answers they deserve."
Mr Spencer said: "As much as the House and I want to find the actual cause of this die-off, we have to face the scientific fact that we may never know, if that event doesn't repeat itself, which I sincerely hope it doesn't, we may never find the cause of that event.
"But if it is repeated then those scientists are ready to jump into action at great speed to try and establish the facts."
However, Shadow environment minister Daniel Zeichner asked why the government had not committed to a further investigation and accused them of "dithering".
He said: "Why is it that 15 months on they still don't know? Is it because we have a Conservative government and a Conservative Tees Valley mayor who have been missing in action?
"Is it because they aren't interested in uncovering the reasons behind it and are more concerned with trying to brush this issue under the carpet?
"Or is it because their priority is protecting a narrow political agenda rather than the interests of the people of Teesside and North Yorkshire? Or is it all of the above."
'Best scientists in the world'
Responding, Mr Spencer described the suggestion as "outrageous" and accused Labour of "playing politics with this disaster".
"There is a shared desire across this House to try and find out what caused this die-off. It has been catastrophic to that industry," he said.
"We have had the best scientists in the world looking at that. We are blessed with some of the most expertise in the world in terms of aqua science looking at this.
"And unfortunately the way science works, is it is very difficult sometimes to identify exactly what is the cause. It is of course possible to rule out what it isn't. And that's what the expert panel has done."
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