The Manx Wildlife Trust says it's worried about the potential impact of silt from Peel Harbour being dumped at a site near Poortown Quarry.
The silt is thought to be contaminated with heavy metals.
MWT Director Duncan Bridges says no independent environmental impact assessment had been done - only an internal one by government.
The Trust also raised concerns about marine pollution when government originally said the sludge would be dumped at sea.
Mr Bridges said there are concerns about that, too:
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