MADISON, Wis. (AP) — A recent report finds around one-third of participating ports in the United States and Canada, including those in Duluth and Milwaukee, are keeping a detailed inventory of greenhouse gas emissions.

The tracking is part of the Green Marine environmental certification program, Wisconsin Public Radio reports . The voluntary effort was formed in 2007 for the Great Lakes and St. Lawrence Seaway.

West Coast program manager Eleanor Kirtley said the program has seen a 12% increase in the number of participants, which includes ship owners, shipyards and port authorities. The program’s overall mission, she said, is to advance environmental excellence among its 133 participants.

“We focus on continual self-improvement,” Kirtley said.

The participants conduct self-evaluations that are verified by a third party regarding their performance on efforts to reduce the risk of invasive species, greenhouse gas emissions, spills, waste and cargo losses. They rated their performance from levels 1 through 5. Lower levels represent monitoring of regulations and best practices and higher levels reflect the incorporation of new technologies and excellence in leadership.

The Duluth Seaway Port Authority, which manages facilities at the largest port on the Great Lakes, maintained a rating of level 4 or higher on areas like minimizing spills, cargo losses and environmental leadership. Jeff Stollenwerk, the port authority’s government and environmental affairs director, promised improvment in areas like waste management and greenhouse gas tracking.

“We’re evolving from a system that pretty much focused solely on carbon dioxide emissions,” he said.

Port Milwaukee, the program’s only participating port in Wisconsin, has also been upgrading its environmental leadership and taking more inventory of emissions produced by their equipment and buildings over the last several years, according to Brian Kasprzyk, port field engineer. He said there’s always room to grow.

“We still need to do some work as far as documentation and some policies and actually getting it in writing,” he said. “A lot of the stuff we communicate verbally with our tenants.”