The organisation, Fishermen and Friends of the Sea (FFOS) has released photos of dead fish in Chaguaramas near to the Crews Inn marina.
The group says the fish were seen floating in the water today and it's questioning the reason behind it.
In a statement issued to the media, FFOS says it wants to know if the Petrotrin spill has any role to play in this latest development.
FFOS is calling on the Minister of Energy and Energy Industries, Franklin Khan, to "please come clean and share reliable information as to how much oil was in Tank 70 prior to and after the rupture on Sunday 23rd April, 2017 and how much COREXIT was used".
FFOS says it is concerned that there is a "massive cover-up" involved.