A CLASS action filed by commercial fishermen in the Supreme Court of Queensland will be "vigorously defended" by Gladstone Ports Corporation, which says the claim is without merit.

It is the fourth class action filed against GPS regarding the Western Basin Dredging and Disposal Project in Gladstone Harbour in 2011-12.

The fishers claim that large-scale contamination from toxic dredge spoil resulted in losses of $100 million.

This latest claim, funded by Litigation Capital Management, was lodged five years after the project's completion.

CEO Patrick Moloney said the class action was a chance for fishermen to be compensated the losses.

GPC chief executive, Peter O'Sullivan said the project was controlled by more than 600 conditions from both the State and Federal Governments.

"GPC developed a fair and reasonable compensation scheme, paying three times the amount of the largest commercial catches for a two year period in each of the four impact zones," Mr O'Sullivan said.

"GPC also established a separate compensation package to enable the promotion of the Gladstone Seafood Industry."

Mr O'Sullivan said numerous reports and independent reviews had all determined that the dredging project did not negatively impact on the health of the Gladstone Harbour.

"The multi-million dollar environmental monitoring program undertaken by GPC for the WBDDP was the largest of its kind ever undertaken for a dredging program, and included independent monitoring across 47 sites in the Gladstone harbour," he said.

GPC has engaged the services of King & Wood Mallesons to act on its behalf.

The three previous class actions were unsuccessful.