Signs 'Deadliest Catch' Star Nick McGlashan's Death Might Be Drug Related

'Deadliest Catch' star Nick McGlashan appears to have died from some sort of drug overdose ... according to police investigating his death.

Law enforcement sources tell us Nashville PD got a call to a Holiday Inn outside Nashville Sunday afternoon. We're told Nick had been discovered unresponsive in his room by a friend. We're told the evidence at the scene "indicated the possibility of drug involvement."

Authorities still need to wait for the results from a toxicology test before making a final ruling on Nick's cause of death.

McGlashan was a prominent figure on the show ... making appearances from 2013-2020. He started fishing at a young age, just 13, and made his way up to captaining boats like the Cape Caution and Summer Bay -- but he battled addiction with drugs and alcohol along the way.