For a sustainability system to improve its effectiveness, address barriers and demonstrate the difference it is making, it must regularly review the outcomes and impact of its activities. This project comprised a comprehensive impact evaluation to assess whether MarinTrust activities lead to improved or protected environmental parameters. It focused on the synergies, challenges and factors driving improvement between MarinTrust-certified and MarinTrust Improver Programme factories. The Improver Programme supports marine ingredient production factories which are not ready for MarinTrust certification to improve their practices towards this.