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.

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

West Coast program manager Eleanor Kirtley says the program has seen a 12% increase in the number of participants, which includes ship owners, shipyards and port authorities.

Kirtley says the program’s overall mission is to advance environmental excellence among its 133 participants.